Well one of the stereotypes of a gamer is a shut-in, generally the type of person who wouldn't go out to play sports. Certainly not everyone on this site fits under the stereotype, but lets be honest, stereotypes exist for a reason, even if they are usually exaggerated. You're right in saying that its strange more gamers don't like sports though, because a lot of gamers are competitive, and sports are competitive.
In my case, I don't like sports because I'm not competitive, and likewise I rarely play any multiplayer games unless they are exceptionally fun because I'm not a competitive player; So I'm one of the oddities of the gaming community which extends to my daily life too. I also just find a lot of sports very dull and can't understand the appeal of them, and I especially hate the sports that are 'rough' like Rugby or Football
I do like Tennis though, but only if I'm playing against a friend and s/he isn't a competitive player either and we're only playing for fun. I dislike it when people can't stand to lose, put all their effort into winning and throw quips or insults to the opposite player (even if its only playful it still annoys me). All I want is a casual game.
I also don't understand the people that watch their country playing a sport on TV and get really into it like its really important they win, and swear and shout at the TV. I find that pretty funny, but I'm just sitting there wondering what the big deal is. I don't give a shit if my country wins anything, my country isn't ME. Then again I've never understood patriotism either.