The kneeling this is simply a reason for people to point to for why they're not watching. The real truth is it's too expensive, it's getting boring, and there are a million other things to do. If those issues didn't exist, people would be watching. They'd complain about the kneeling, they'd make those players into heels to root against or others would make them into heros and they'd simply go at it. The real truth is it's simply getting boring, the players now are all just "professionals" without much fire, and so many rule changes have taken that fun and spontaneity out of it.
I don't know how you "Fix" it. You can't go back to just letting almost anything go when it comes to tackling as it was in the 80's and before. We simply know too much about the sport, but it was that type of play that kept the game fun. There were also great attitudes and personalities to root for and against. The NFL has fined people so often for showing any personality on the field that now they're all just clones of one another being "professional".
That might be a place to start. Cut down on penalties for celebrations, taunting, etc... That's all part of the game. I know it doesn't make the players great role models, but it was fun. The league needs a few Warren Sapps to bring some personality and swagger back into the game again.