Well, it's different than the usual type of thread heh. Anyway, you can't group everyone into the same likeness. I remember seeing a profile of a bodybuilder built guy who was looking for a heavy bearish guy so anything is possible.
But if I had to guess... It's probably because a lot of jocks and those that workout/take care of themselves aren't turned on by fat/heavy guys because they feel like they don't take care of themselves. Now, I know it's possible to be big and eat healthy and all that, but I'm just speaking from a general view a lot of guys have.
But seriously, I'm sure there are said guys out there attracted to bear-type men. Heck, I've noticed that quite a few jocks would rather have a guy with more meat on his bones than someone who is skinny/slimmer. Believe me.
Just be patient. There are "chasers" out there and while they aren't very common, they do exist. But of course, if you aren't meeting the guys you want, you can always workout yourself if you want to.
I mean, as much as I like being lean, I realized that in order to attract the guys I like, I have to change my body a bit. I still plan on keeping my lean build but just toning and adding a teensy bit of mass to fill out a bit. But then again, it's something I wanted to do for myself. So if you plan on changing your appearance, make sure it's what you want.