While the comparison to movies or opera is interesting, it’s also problematic, and I think the lack of appeal sports has to some is rooted in some of the fundamental differences between the two.
Yes, sports have incredible potential for great drama and unexpected surprises. But most games do not provide this. There are selected moments of tension and excitement and bursts of energy, but like most of the conversations I have every day, “unscripted” sometime means boring or inert. Yes, lots of stuff is going on, but it doesn’t necessarily amount to much, or the result can be disappointing and anti-climactic (but not in a cathartic way that drama’s “unhappy” tragedies can be).
Great drama aspires to teach about the human condition, but most great sports aspire to convey human achievement (largely physical, sometimes tactical). Both noble pursuits, but not really the same thing, and I’d say the latter is more limited in its accessibility.
Another important difference is context. Unless you’re schooled in the histories of the teams and the behind-the-scenes situations of the individuals, most of the players are interchangeable to the casual spectator and the inherent drama of a given situation (a streak, a slump, a comeback, etc.) is lost. Most scripted drama (with the notable exceptions of soap operas & pro wrestling) usually assume you know little or nothing about the characters you encounter, so they make the effort to orient you with the conflicts and personalities.
Sitting down to watch a game cold, none of this contextualization occurs. Nothing wrong with that, but what it does mean is that to fully appreciate a dramatic situation in sports, you need to invest more time and effort beforehand. Not everyone is willing to do that, and thus the appeal of most sports is going to be more conditional and less universal.
Also, a negative experience with a dramatic presentation can usually be attributed to something or someone–an actor, director, writer, etc. That’s usually not true with sports; sure, sometimes there’s a “goat” or a player or squad that underperforms against expectations. But I’ve found that a lot of sporting events that are letdowns (or at best, unmemorable) are such because everything more or less goes the way you expect it to–the favored team wins, the good player delivers, the early lead is established and never threatened, the so-so player chokes like usual. Given this, a truly great or transcendent game often proves itself to be the exception more than the rule.
I’d speculate that more people tend to watch playoffs and championship matches because they assume the law of averages is in their favor that they’ll see a competitive game. But many of those same people can’t be bothered with the months leading up to that, because they’ll see it as not worth the time and effort. A truly phenomenal game may come out of nowhere from the most unlikely of places, and such a thing is truly special, and the elation from that may make the previous few weekends’ same-old/same-old worthwhile. But not for everyone.
Although dramatic presentation appreciation can benefit from being in a group, I also don’t think it’s nearly as important as with sports. The energy of a full stadium, the noise of the crowd, the civic pride you communally share with fellow fans who are otherwise strangers–these add to the dramatic context of a sporting situation, often critically. I love watching baseball games in person, but rarely do at home alone on TV. I think the difference between seeing a game at home and in person is far greater than the difference between watching a movie at a cinema or on a DVD, and a lot of casual viewers (or “non-fans”) have a harder time bridging that divide.
So, essentially, while the “everyone likes different things” point is a fine and valid one, I think you have to admit that there are a lot more variables at play when it comes to enjoying sporting events than other things, and the accumulation of those variables make a non-sports watcher more alienated than non-watchers of other pasttimes. This is not to say that sports are elite or rarefied (obviously not true), but they have different barriers that make them inaccessible to some in ways that are unique.