I would speculate that the degraded coach experience has a lot to do with the airlines' ability to monetize the front of the plane.

Maybe I am getting old (well, I'm definitely getting old), but I can honestly say that flying economy has gotten a lot worse since I started flying almost 25 years ago. I am old enough to remember free meals on domestic flights in coach... boy those were the days.

Despite all the ballyhoo around cleanliness during COVID, I've found the coach cabin to be filthier now than ever. "Turbulence" preventing in-flight service has become commonplace. Ordering one drink gets you the stink eye from the cabin crew. The seats are thin and don't recline as comfortably as the past but yet still somehow encroach on your space when the row ahead of you decides to recline.

I can see why more passengers would pay for F, particularly if it's dangled in front of them at T-36 in an email or app alert, or at T-24 at check-in. Especially if the price is reasonable, it can be a good way to avoid what economy has become. That of course means there's less space for elites.

I'm at the point where I pay for the class of service that I want at the time of reservation, and if that means flying less so I can afford my desired cabin, so be it. That typically means J for int'l itineraries and some kind of premium class/C+/E+ for transcon domestic routes. Loyalty to one airline is overrated, go with whoever has the best combination of price/route/time/product and just pay with cash or miles for whatever experience you want.