My guess is this:
1. No zero or low value, pointless or uninteresting posts or threads. [1][e]
I would say that forum moderation tends to be quite strict in terms of posts that doesn't really add to the discussion (I know there isn't a lot of discussion in the collectibles anyways). It would be quite detrimental to the forum if all the account botters flocks to collectibles and starts spamming useless posts.
I don't think it's particularly fair to remove posts that express gratitude but perhaps giving a merit would be better.