All the stuff cited here is valid, but I'd throw in increasing ambivalence about football itself as another factor. I still enjoy watching it, but as awareness of CTE, opiate addiction and other long-term consequences rises, it's hard to just sit back and pretend it's simply good fun entertainment. Especially when watching unpaid young adults.
I'm a former season ticket holder, and I will attend at least two games this season, but my interest has been waning for years. I doubt I'm alone.
Your last two sentences also apply for me, though I currently retain my season tickets. If it weren't for the fun I get out of tailgating and spending fall days in Athens, I'm not sure I would continue with season tickets. But the entirety of the gameday experience in Athens keeps me coming back.
The Game of Football isn't nearly the draw for me that it once was. College games, while providing a great atmosphere, and probably more entertaining game (when games are close), still takes an eternity in the modern era. Replay reviews, the fact that many teams throw the ball a ton, and TV timeouts all add to the length and slowness of many games. Other contributors for me include trying to sell my non-football fan wife on the idea of sitting on metal bleachers in the hot sun for nearly four hours. Another factor, for me, is the no re-entry rule. I like leaving for the third quarter to be able to return for 4Q and to see the band for post-game.
But in person games aside, I also don't watch the game as a whole the way I used to - especially the NFL. I no longer invest 6-7 hours per weekend day watching football on TV the way I used to. For me, because of the research done on CTE, and the way they've (correctly, mind you) legislated hitting out of the game, it's just less fun to watch for me.
I've been of the mindset for a few years running that "Football is for tailgating". Even if I'm not at a game, I'm probably most likely to watch in a social setting.