I suspect that part of the problem is that airline seats aren't advertised in a way that allows consumers to effectively comparison shop. Consumers aren't aware of or can't tell the difference between the "economy" seats offered by different airlines, and so there's a race to the bottom.

Imagine if regulation required describing the seat with a couple of factors such as the "pitch", the width of the seat, and/or the total volume of space dedicated to the passenger. When shopping for tickets, instead of displaying purely the cabin class, the tickets would be characterized by their space and comfort (measured objectively).

Consumers might think twice before selecting the ticket that's cheaper by $25 if they can see up front that it has 3 inches less legroom.