The complete rule snippet relevant here is:

Material (M)

Casting some spells requires particular objects, specified in parentheses in the component entry. A character can use a component pouch or a spellcasting focus (found in chapter 5, “Equipment”) in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.

First of all, component pouch and focus are mechanically the same, and used "in place of" the listed objects. The non-intuitive, but notable detail here is, that the component pouch does not contain the components listed in the spell, it contains the components needed to cast the spell, when you use the pouch in place of the material component. To verify this, let's see component pouch description:

A component pouch is a small, watertight leather belt pouch that has compartments to hold all the material components and other special items you need to cast your spells, except for those components that have a specific cost (as indicated in a spell's description).

This small pouch itself is not said to be an extra-dimensional space, and has a fixed weight, so it most certainly can not contain 25 feet of hemp rope for Snare, for example. Another example, storing a cup of water for Armor of Agathys in a small pouch seems a bit impractical. The only reasonable conclusion is, that at least some of the stuff in the pouch is different from what is listed in a spell's description, while still being as valid as a focus for casting the spell. The pouch is not some mysterious storage for literally every listed zero-cost material component of all spells. What exactly it contains is left for DM to decide, if hand-waving of "everything you need to use the pouch in place of the material components* is not good enough.

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Then there is "But...", exception for components with a cost, which we don't care about in this QA.

Then the second paragraph seems a bit redundant, but since it is a separate paragraph, with no "Additionally..." or anything else linking these things, it must be about something else than the previous paragraph. I guess it's meant to prevent certain shenanigans, such as two wizards casting Find Familiar at the same time, with same components, for half the cost, or doing several Snare castings from a single rope (hemp rope is surprisingly heavy to carry around). Not really relevant for this QA.

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So we are left with: You can use a component pouch or a spell casting focus in place of a material component, if it does not have a cost. Let's do so!

Snare ... Components: V, S, M (a component pouch or a spell focus, which is consumed by the spell)

Looking through the rules, I can't find anything, would stop the spell from consuming the component. The pouch or the focus takes the components place in the casting of the spell, which requires it to be consumed.

Conclusion

If you use a component pouch or an arcane focus in place of a consumed material component, then the pouch/focus is also consumed in place of the material component.

It also makes narrative sense. Consider making a homunculus. The material of the homunculus needs to come from somewhere. You'd need the 9th level Wish to make it materialize out of thin air.

Consumed components must be provided; they cannot be replaced by a component pouch or focus

The rules in question are these:

Casting some spells requires particular objects, specified in parentheses in the component entry. A character can use a component pouch or a spellcasting focus (found in “Equipment”) in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell. [...]

From the first part, we can conclude that component pouches and foci can replace material components, but not costly ones. From the second part, we can conclude that consumed components must be provided. There is no contradiction here. Pouches and foci can still replace material components, just not ones that are consumed or priced.

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You can also think of this as specific beating general: in general, component pouches and foci can replace material components; however, in specific, consumed components must be provided and thus cannot be replaced with pouches and foci.

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Personally, the adjacency and similarity of these rules is what sells me on this conclusion. The rules go (basically) directly from stating one restriction to stating another:

[...] if a cost is indicated for a component, a character must have that specific component [...]

[...] If a spell states that a material component is consumed by the spell, the caster must provide this component [...]

There is no meaningful difference to me between the wording of these rules, so I would not interpret them differently. Thus, component pouches and foci cannot replace costly nor consumed components.

RAI: They are consumed

Because there are three places that talk about consumables, foci and pouches, and they seem to disagree, we must look to the intent of the game designers. When Asked:

@JeremyECrawford Can Protection From Evil and Good be cast with a component pouch or a focus?

Reference to holy water makes me think no, lack of price makes me think yes, the fact that it's consumed makes me think no again.

Jeremy Crawford replied:

If a spell consumes its material component, you must provide that component every time you cast it. #DnD

And here again, Jeremy Crawford states:

@jackAbrasion A spellcasting focus can't substitute for a component that is consumed.

So, the rules as intended by the designer is that they are consumed, and the pouch doesn't just have an endless supply of these consumables. He did add:

The cost isn't a concern for that spell, only that you have some of the material for the spell to consume. It's a narrative device: sprinkling holy water or the powder.

So, a generous DM can run this the other way, without breaking balance. Items with cost, however, could break balance.

Yes; a focus can substitute for zero-cost consumed components.

tl;dr Foci and component pouch both have the same function in replacing non-cost material components. Component pouch contains all the non-cost components including consumed ones. So the foci can be used to substitute for non-cost consumed components as well.

Non-cost consumed components are infrequent.

There aren't many spells that specifically call out non-cost components that get consumed. Some examples are magic mouth consuming the honeycomb along with the jade, speak with dead burning incense, and _globe of invulnerability_ shattering a glass bead. The vast majority of spells that consume components specify a cost for all the consumed components.

Apparently conflicting rules from casting a spell

If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.

Versus

A character can use a component pouch or a spellcasting focus (found in “Equipment”) in place of the components specified for a spell.

Component Pouch

Found under other adventuring gear states that is has all the components needed to cast your spells. The use of "all" supports that it includes sufficient amounts of consumed non-cost components such that they can be effectively eschewed.

A component pouch is a small, watertight leather belt pouch that has compartments to hold all the material components and other special items you need to cast your spells, except for those components that have a specific cost (as indicated in a spell's description).

Both rules are more specific than the general case.

Specific beats general. In this case, both rules are more specific than then general case of the caster must supply the material components of a spell when casting it. Even if more specific beats specific, it is still not obvious which rules are more specific than the others.

No, you need to supply the material component.

Consumed components require the material component to be supplied in the same way that components with a value must be supplied.

From the Basic Rules (and PHB, 203)

If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.

There is no contradiction here - this is a specific rule regarding consumed components that overrides the general focus and component pouch rules. The component and pouch rules apply to all spells, but the specific rule cited above is specifically for spells requiring a consumed component.