You have self moderated threads which allows the OP to delete unwanted posts. However most self moderated threads that are active in deleting critical posts are scams, this would only make it easier for scams to be successful.

The most common legit reason why OP's of self moderated threads delete posts is because they are spam. It would be possible for the same person who spammed a thread to later make a legit post with good points.

All threads are moderated, just not self moderated