Just as like most of the bounty hunters, who only care about their post quantity...
I don't know why they try to post in spam megathreads, those are periodically get deleted...
If they would just post in off topic, they won't lose a post...

I often think about creating one megathread in the off topic section for those who only want to gain activity, e.g.: post here to increase you post count and not to bother the other users on the main boards...

In that case they would have a topic where they can spam and the forum would be free (or nearly free) of spam...