This is one of the weirdest threads I've ever seen on any forum. Not the weirdest one, but I'd say it goes in top 10.
Okay, my 0,20 monetary units come here:
What Makes Baseball, Basketball, Volleyball and games like these boring: High learning curve. It's not easy to play these well, and if you don't know how to play well - OR you're in very good company that doesn't care about the results - it's just plain boring to play these games.
On baseball you have to be able to both hit the ball and catch it, both of which take time to learn. And while playing these games, most players are just idling and waiting their turn to hit, or if they are on the field they're idling and waiting for the ball to come to their approximate location. I've played Finnish baseball in school and it is just plain boring when the players are mostly not playing it as a hobby... and watching baseball is even more dull. Basketball would be slightly more interesting to watch, but it happens to be a small sports here so I couldn't really give a damn of the results so it becomes just as dull as baseball. And it's boring to play if you don't practice it and become good at it. Same applies to volleyball.
On the other hand, a sport like football is very easy in basic principles and it's a lot easier to enjoy just playing the game even if you're not pro. So, football is nice to play I'd say... but most of the time it's quite dull to watch if you have no affiliation with teams.
Ice hockey and ice ball and such are also nice to play while youve learned skating. Plus it's quite more fun to watch than football... though that depends also a great deal of many things, of course. Bad hockey game can be worse to watch than a mediocre football game.

American football I know nothing about. Though it definitely doesn't seem as much fun to play with random people like, in school lessons.