This is already the answer the forum best can give. Managing spam on the entire forum with only a small list of mods is very difficult and I doubt they would even search for such spam willingly. Just the amount of replies a thread can be astounding already, what more the countless parts of the forums here.
Besides, most spammers are just newbies accounts and wouldn't even think twice of creating another if they get banned. This just makes it an endless process and seems useless to do so they might as well just let users report spams they see and mods would then take action then and there.