Maybe it's related to declining activity on the forum, so even those spammers are seen as a necessary evil to keep the forum active. Beggars can't be choosers. 
If theymos wanted spambots to keep the forum active, he could just as well make them by himself. I doubt he's into that.Why even bother replying to this topic? Yet, it has over 40 pages of replies.
Spam megathreads work great for reaching post quotas. That's 800+ posts about nothing, read by nobody, but all being paid.