In the case of SWTOR, my main was a trooper. I made him body type 3 because the voice doesn't really seem right to me on a body type 2 and the look I was going for on my trooper didn't really look well on the 2nd body type. Also, since I went commando, it only made sense to be some massive soldier.
To answer your question for games in general, most male characters are made to look strong and physically fit because it's more epic. Smaller characters are looked at as weak and less appealing for quite a few of roles. You wouldn't want someone in a military game to be small, would you? It wouldn't make much sense.
If you want to see less bulky characters, find a game with spell casters and stealthy classes where the character being smaller makes more sense for that role.
Just the way I see it.