This whole war on spam/bots/or malware is like football game, when only one team has gate (and without gatekeeper). This team is Epic mods, Forum Owners, AV companies.
First there are more people that try to exploit than people that defend, esp when attackers can get some gain from it.
Also defender cannot respond proportionally, well cannot respond at all, can just defend. Banning bot accounts is just defense, bad guys can create multiple bots. Epic cannot do any harm to actual creators.
Same goes for malware detection, AV can only defend and response. All attackers must do is update detection, and try new mutations until it fails. Same would happen with automatic detection of spam. They get banned automatically for few days, in that time they improve creating new ones, banning script fails, and bad guys just improved botnet.