Because I like my creations the way they are, rather then being mutilated by other people sticking their oar in where it isn't particularly wanted.
I can't remember ever having tried to suggest changing someone's character or their background, because I think doing so is really insulting the person. Regardless of whether they are offended or not, I don't like it, so I don't do it. Just because everyone else doesn't take offense doesn't mean I won't either.