There's a big reason that people breed animals to be obese. I grew up on a sheep and chicken farm. And to be honest, a lot of people would not eat those animals. They are lean, and gamey. Not like anything you would buy in any store.
Personally, I love it, and it makes me sad that I can't buy anything like it in NYC. Not even stuff that claims to be cage-free or organic or whatever. You just can't get that stuff here.
But it has a lot less fat than what you buy in the store. Fat is basically flavor for chefs. Whether it's butter or animal fat or vegetable oil, fat is where it's at.
The more obese an animal is, the better it's going to taste when you cut it up and cook it. That's just an unfortunate truth. When there's a market for something, people find a way to produce it.
The market is for massive amounts of white meats with a lot of fat you can render. That's what people buy, so that's what people sell.
Funny you mention this, as recently I accidentally bought an older chicken at the store (a younger one half the size was the same price).
It probably would've worked for coq au vin, but roasting it was a bit of a mistake - meat was quite tough, although I turned it into an okay salad