Finally, I found this great essay on Grantland which answers exactly my questions.
First, why is soccer so dull?
There are two reasons, basically, why soccer lends itself to spectatorial boredom. One is that the game is mercilessly hard to play at a high level. (You know, what with the whole "maneuver a small ball via precisely coordinated spontaneous group movement with 10 other people on a huge field while 11 guys try to knock it away from you, and oh, by the way, you can't use your arms and hands" element.) The other is that the gameplay almost never stops — it's a near-continuous flow for 45-plus minutes at a stretch, with only very occasional resets. Combine those two factors and you have a game that's uniquely adapted for long periods of play where [the ball bounces around chaotically and nothing seems to happen]...Second, if soccer is dull, why is it the world's most popular sport? Why the crazed fans?
Following soccer is like being in love with someone who's (a) gorgeous, (b) fascinating, (c) possibly quite evil, and (d) only occasionally aware of your existence. There's a continuous low-grade suffering that becomes a sort of addiction in its own right. You spend all your time hoping they'll notice you, and they never do, and that unfulfilled hope feels like your only connection to them. And then one day they look your way, and it's just, pow... I watch soccer to be amazed.Oh, and check the footnotes of Brian Phillips's fantastic piece to hear his meditations on how American sports (football, baseball, etc.) have rules which promote regularity and prevent the kind of chaos observed in soccer.