Most of you (actually all of us) just got older. Unless you are incredibly passionate about a sport, there is a novelty factor to all of them. You can only see so many dunks, 3 pointers, home runs, touchdowns before it really doesn't do much for you anymore. Throw in the fact that entertainment options were way less in number a few decades ago, you probably spent a lot of time watching sports that you maybe weren't as enamored with as it seemed.
I don't watch any baseball, hockey or college sports now. I just grew out of them. I don't really care who wins and I don't bet on those sports so why would I watch them. I don't think they've gotten worse, when I catch 5 minutes of an NHL game guys are flying around like mutants on skates. It looks way, way better than when I actually did watch. College basketball has gotten worse, but college sports was always a flawed model. Minor leagues would be better but then the fan passion isn't there because people love to root for their alma mater or local school. It is a market distortion in a sense.
Something like baseball is almost the exact same as it was 25 years ago, very little has changed about the game. You just don't feel like spending 3 hours a night watching a game. Your attention span just isn't there to watch something like that. It's a slow game in an increasingly fast paced society.
A few times this year, the primetime stand-alone NFL games the score would be like 16-13. And people would post like this was the worst thing in the world, like it was an abomination that nobody was scoring. You know how many games used to be like that? A much higher number. Watching an old NFL game is like watching a Charlie Chaplin movie, yeah you appreciate it but it is also horribly dated.
People talk about the officiating in the NBA, but it was always inconsistent. Go watch a game from the 80s, it is an endless parade to the free throw line. That is all they do all game is shoot free throws. Significantly more FTs were shot back then than are now. If people had the attention spans then that they do now, they would've turned the game off in the 2nd quarter every single night.
Boxing has gotten worse, a big reason for that is the other sports salaries skyrocketed so much that nobody is trying to box from the time they are 8 years old anymore. And that is really needed for mastery of the sport.