There are other causes as well.
The games nowadays take 3 1/2 hours to play. There are far more commercials on the games now than years ago.
We live in a culture in which people seem to have shorter attention spans. How many sit down to watch a 3 1/2 hour TV show of any kind?
Nowadays, all TVs have remote controls, which make it easy to change channels, and click away from the game during the interminable commercial breaks. With more channels than ever before, some people may find something of interest and not get back to the game.
It’s tedious to watch some games, what with continual commercial time outs, so many penalties called, which stops the game, time consuming replay reviews.
And don't forget the MUTE button. Oh, how I love the MUTE button.
I’ve gone with family to see my niece’s softball games, I’m totally good spending 3 hours doing that. Seeing a pro football game on TV is just an annoyance, I can’t watch that crap, which is more commercials than not. I also like to take my daughter to the college hockey games at a nearby college, which costs us a total of $6 to get in.