>>24532981 (OP)I don't know that they are. Some are. And some non-writers are, too. Are you saying that a much higher % of writers are misanthropes than non-writers?
It's easier to judge how many writers are, because writers tend to write down how they feel about things; non-writers don't.
Anyway, if what you say is true, here's one possible cause:
Writing is a solitary activity. You are more likely to want to be solitary if you dislike people.