Why are bicycles so expensive?

As stated in the comments, your main sport is a strength sport, so I assume you are looking for a bicycle to commute or to do some light aerobics on.

It's not clear which store you shopped in. There is a wide range of price points including many much lower than your stated range. US$5k will get you a mid- to high-end performance-oriented bicycle. Here, I use Specialized bicycles not as a product endorsement, but because they were the first name that came to mind and they are one of the largest US brands. Their fitness line contains the Sirrus line of flat bar bikes. MSRPs for new current model bikes range from $650 to $2,600. You could easily commute and do light aerobics on this type of bicycle. The Specialized Diverge (technically a gravel bike, but totally usable on the road, and can take cargo racks and fenders) does indeed have a version that costs $10,500. However, the base model is $1,300. Many of the major bicycle brands, like Giant, Cannondale, and Trek, will have similar bicycles to these types in their lineup.

You may also have been thinking about electric bikes. Because of the battery and the motor, these are inherently more complex and expensive than non-electric bicycles. I am not familiar with e-bikes, but I think that a more basic e-bike can be had for less than $5k.

The target riders at $4k and higher are serious cyclists who have disposable income and who have been cycling as their main sport for a long time. Should you wish to get more competitive as an endurance athlete, I can say as someone who owns more than one expensive bicycle: it's mainly about the athlete, not the bicycle. Almost every cyclist on a $5k bicycle will have been beaten by a younger cyclist on a cheap bicycle - and many of them were once the strong young cyclists on cheap bikes. You would almost certainly be left behind if you showed up on a department store bike (barring professional-level talent), but once you are on a decent bike, it's your body which holds you back.

Tackling the question in the title, I realize that even $1,300 seems like a lot of money for what seems like a simple machine. Bicycles are surprisingly complex. For someone familiar with bicycles, there are a bunch of important components where the better choice simply has to cost some amount of money. For example, the brake pads on many cheap rim brakes are garbage. Actually, there are excellent third party replacements available for not much, perhaps US$20 at retail, but that would still raise the bottom line cost for the manufacturer. There are the bearings and seals on the hubs and in the bottom bracket and headset. There's a bunch of stuff. I imagine that you can still get a cheap motorcycle for the cost of an entry-level bicycle, and I would imagine that the answer there is that bicycles may have poorer economies of scale. In any case, given your stated use case, we can make one recommendation that should keep your costs lower: you don't need a suspension fork. Your tires offer adequate suspension for your use case. If a manufacturer specs a suspension fork for a bicycle which doesn't need one, that a) reduces the amount of money they have to make the other components better and b) it adds to your maintenance costs.

TL;DNR - Bikes are so expensive because people are prepared to pay that much.

Pricing of the product is a balance of the cost to supply and value add to the customer. In the perfect capitalist's world, a product is produced for nothing and sold for as much as each individual customer is prepared to pay. In (arguably disproven) theory, competition will drive the price down to the cost of supply, and drive efficiency in the supply chain lowering the cost of supply.

Cycling is the new Golf, cashed up MAMILS (Middle aged men in lycra) are setting the sell price, however, MAMILS don't buy just anything, they are paying top dollar, and expect the best of the best for it. The manufacturers have responded by supplying bikes that are the best of the best.

The profit from selling a $10000 bike is far more than the profit from selling a $1000 bike, so marketing and sales - from the subliminal images in advertising photos to bike shops upselling is aimed at getting you to buy the most expensive bike they think you can afford. Its blatant on one front, and subtle on the other, you think you have not been sucked in and settle for the $5000 bike instead of the $10000 bike, when a $1000 is all you need.

Note this is not a statement about wrongs and rights of people buying nice bikes, nothing wrong with those who can afford it filling their boots and buying a $10000 bike, or 'settling' for a $5000 bike. Its in the industries interests to sell lots of those bikes. Its up to communities like us to push back against the marketing and present a concept to people - you do not need to spend $10000 to get the bike you need, and help people understand the difference between need and want.

To use car sales analogy. If you go to a Ferrari or Lamborghini dealership, all you'll see are cars for $1 million or more. If you go to a used car dealership, you'll find quite different cars for $5000 or less (I actually have no idea how much cars cost in USA). If you want to settle on something middle range, you can find something at just about any price point.

It really has nothing to do with bicycles. It is common economy principles applied to any type of freely marketed goods.

Some example from Austria and Germany for new bikes:

• ~300€ will get you a cheap city/trekking bicycle with the cheapest components and 3x7speed gears. Often not assembled properly, low quality and heavy.
• ~600€ will get you a solid brand-name city/trekking bike or cheap MTB.
• ~900€ is where real road bikes and MTBs start.
• >1300€ here you get good aluminium frames and Shimano’s or SRAM’s mid-range components.
• >2000€ carbon frames, upper mid-range components. From this point on you mostly get improvements in weight.
• >4000€. The best of the best. Road bikes with electronic shifting, aero wheels, <6.8kg weight etc.

I think for the US you can just replace € with $. Of course prices depends on region, discounts etc.

I don’t think bicycles in general are particularly expensive, you probably just looked in the wrong place.

As Pere points out in the comments, used bikes are often a good idea, especially when you need a cheap (<300€) bike. But in my opinion you should have some knowledge about bike fit and bike mechanics to be able to properly evaluate (and repair/maintain) a used bike. Sometimes good bikes are sold as “broken” for a few dozen Euros despite only needing some adjustments, a new chain and new tires.