I'd probably watch it and go to the SB parties if it weren't for the weird as hell culture around it. Like, I don't get the whole "my team" thing, or how passionate people get. It's worse in Europe with Soccer, though.
It just baffles me to no end. It's supposed to be entertaining, not life affirming/changing.
Well, look at your average Joe Sixpack. Middle class, probably working a dead-end job, graduated high school in many cases but only a few might have an associate's degree or some miscellaneous college credits, even fewer have a bachelor's. Raising two or three kids, might not have much by way of hobbies because they can't spare the time or the cash. Probably married young, divorced within ten years, might or might not have remarried. Went to a high school that had a football team, possibly baseball and basketball as well (hockey on occasion but not often and generally in colder climates where the sport is popular), and if they didn't play for "their team", they at least attended pep rallies and rooted for them.
For this common stereotype, high school was probably the peak of their lives, at least in terms of a general state of happiness or well-being and having a feeling of belonging. They remember how happy they felt having their "heroic" athletes defend the honor of their school, and they transfer that to a favorite sports team, usually local. They might have many different teams they root for in different sports - usually there's a cycle of baseball, football, and either hockey or basketball, so at any given time during the year, at least one of their team's sports are in season.
In a strange way, you could compare it to the otaku phenomenon, except that popular sports such as those are considered more socially acceptable. Go somewhere dress completely or partially in a sports team uniform, you're considered "normal", but go around in a Starfleet uniform, superhero costume or wearing a cosplay outfit, you're considered different - not one of the "team" - and by extension you're someone to be at least wary of, if not act anti-social towards in an active way. Sports guys obsess about their games and teams like anime fans obsess about their characters and storyline (and perhaps fan service!), or we obsess about playing cards, or a comic book reader acts about their favorite superheroes.
When these sports became established and popular in American culture, there was a lot more general conformity in society. Breaking with that conformity was always subcultural until around the mid-1970s, when full-blown hedonism became popular. Before that, yes, there were speakeasies and jazz clubs, then beatniks, followed by hippies - but by the mid-1970s it was all about making yourself happy and to hell with the rest. This fracturing of the conformity continues to this day - and is coming full circle, as standards of conformity develop within the subcultures!
But there are still enough people who stayed with the old mainstream conformity, who followed their high school teams, then maybe college teams, all the way up to the pros. The companies behind these franchises do everything in their power to build up that conformity until for some, it's practically cult-like. This was very easy to accomplish in the days of mass media such as radio and television. Now, they use the Internet because it's there and practically everyone in the Western world uses it - it's simultaneously their best friend for spreading sports popularity and creating more fan participation, and their worst enemy for providing people with a near-infinite number of outlets for entertainment.
OK, I think I've rambled enough for one night...