What makes frozen burger patties bland?

When you buy a burger from a fast food restaurant you are buying a product that has been engineered to provide absolute consistency, be very fast to cook, and be as cheap as possible so it can be offered at a low price for a reasonable profit. The grill marks are engineered in, and they are given coatings which will give the right appearance when cooked. They also have flavorings added so they taste as the designers (yes there are burger designers) intend. It's not a simple bunch of ground beef at all. Most frozen pre-made burger patties are similar, they use cheap cuts of beef (and sometimes reclaimed meat) and artificial ingredients to produce a consistent and inexpensive product. They also tend to be very thin and are easy to cook all the goodness out of by accident.

If you want a really good burger then you need good burger meat, it's as simple as that. You can't make a good burger out of low quality meat no matter what you put into it. The simplest way to make a good burger is to find a local source of good quality ground beef and make your own patties. Making patties is very easy and quick, just get your hands in there. Many supermarkets have perfectly good packaged products (I get mine from a local grocery store and it makes good burgers), so that would be my first port of call, next would be butcher shops.

If all else fails and you want to make your own (or just give it a try) then you're in luck because the best cuts for burgers are also the less expensive ones, like brisket, chuck, short rib, and round. Round has great flavor but is very lean, and working cuts like brisket and chuck are also lean, so you'll want to add some fat. Many burger nuts say you need 30% fat by weight, personally I'd aim for 20% as 30% is too much for my taste, but that's up to you.

As for frozen versus fresh, freezing does cause some loss of flavor, however it's not much. You are much better off with frozen good quality meat than fresh low quality.

My first guess was "oxidation". Googling that I found a lot of results.

Here is one blurb about 'Meat Flavor Deterioration':

MFD is initiated during processing procedures such as grinding, cutting, freezing, tumbling, massaging, and/or cooking. Iron liberated from meat pigments catalyzes oxidative degradation of highly unsaturated lean tissue phospholipids. This oxidative reaction differs from triglyceride oxidation (oxidation of fat tissue) in two ways: it takes place at an exponentially faster rate; and the off-flavors produced are different from typical rancid flavors. While off-flavors develop, rich, meaty flavors fade and are overwhelmed by off-flavors produced by oxidation reactions. This irreversable combination of flavor changes constitues the word form 'MFD.

http://www.kalsec.com/services/casestudy-antioxidants/meat-flavor-deterioration/

So, even if you grind the same quality meat at home, the results will be superior to frozen ground meat.

Simple. Lack of seasoning.

Add salt before cooking as well as seasoning. Be liberal with the salt, and don't use table salt, use a salt grinder. The burgers will not be bland. Gordon Ramsay takes this to another level, he even seasons the lettuce. Look up the video on youtube. That's a bit over the top, but the fact is that it's only bland due to lack of seasoning.

It's true that frozen burgers from the store are not as tasty. Especially if they lack fat content. Yet, add enough seasoning and you could make it taste good.