because after signing up you can't do anyting. New users can only watch and comment. Their votes don't count. When a thread will be voted by some new users the

because after signing up you can't do anyting. New users can only watch and comment. Their votes don't count. When a thread will be voted by some new users the thread will be killed and users will be black signed. After some days day can submit something. And the submitted threads are always controlled, killed or downvoted. Fake accounts simply can't spam.