Here’s what I’ve got:
It owns a day of the week, which church used to do for more people.
It’s the closest thing we have to “gladiators” or “warriors” in the modern age.
Regional tribalism.
Gambling.
Fantasy football. (Which is one of the primary, if only, ways that guys retain long-term friendships across distance and children.)
We like violence more than we admit.
A lot of guys (and some gals) like to sit in relatively dank bars, drink beer, and eat crappy fried food for a portion of Sunday to put off the reality of an upcoming workday, so it clicks there too.
You played the sport and like “couch-quarterbacking” it from the bar stool (or your couch).
Food.
Chances to get together.
We like to see new beer commercials and insurance commercials with celebrities in them.
It’s a way to stay connected to friends across distance (i.e. fantasy but also shit-talk texting).
We see the hypocrisy in suspensions relative to violations, and it secretly comforts us because of the hypocrisy in our own lives every single day that we gloss over :)
The players become characters (“I’m a football player for six days. On Sundays I’m an entertainer.” — Chad Johnson)
We like to debate merits.
We like to think we know more than professionals in every conceivable cranny of life, and especially guys who make millions of dollars to play what’s at heart just a game.
What else would you add?
It's the modern American equivalent (with beer) of the ancient Roman "bread and circuses"--i.e., a way to keep the masses fat, ignorant, and happy.