I don't read much SPN slash, more crossover stuff if any. I am a bandslash person (which is a little more wrong, since they are real people)

ANYWAY MY POINT...

I know, at least in bandom, the Het stuff 9 times out of 10 ends up a Mary Sue. Maybe it's the same thing? Lack of females in the show forcing people to "create" their own, and it ends up being them just awesome.

That is my theory.