Well, there are 4 problems with the spammer:
1. It hides behind other IP-addresses, making it impossible to IP-ban them.
2. It makes all the accounts manually (or at least don't seem to have a problem with creating them), so a better register account system wouldn't work
3. Requirement for creating topics would mean new users who aren't spammers would have to do something like that too, which might cause them to accidentally spam threads or something. (Not sure how to explain this, if this point doesn't make sense, that's probably why)
4. A flagging user system that checked the amount of flags a post gets would be possible to misuse.