I agree with you on this fact. My last flight swapped carriers and one had significantly better seats than the other. (This also happened on a regional jet, which I think exacerbated the problem.)

But I think part of it is also location. Some airports are only served by one or two airlines, effectively limiting choice. So the result is that if I wanna get home, I'm stuck riding with the bad airline.

I generally prefer the train when the distance is reasonable enough.