Reason

" and not with fake girl profiles in order to befriend and collect pictures from other girls."

Another possibility for having a fake "girl" account (and the one I believe is more common) is that the guy with the fake "girl" account is attracted to men but doesn't want to admit it. By having a fake "girl" account, they can become friends with other men and develop relationships with other men and have it be "ok."

Yet another possibility is for the purpose of scamming men into sending them money.

And one more, many of those fake accounts provide URLs to porn sites.