Mods do not want to disrupt the mostly useless discussion , that is what I feel as most of it is spam. What they do now is declare a new thread not suitable for the board and move it to another, which I have seen & faced. It is very hard to question them, as my self-moderated thread was moved from the gambling discussion board because it was reported, which I found strange as a self-moderated thread can be only reported to the person who is the owner of it, when questioned.
If you read the first and second page of threads, they are mostly what can be considered as non spamming discussions because only very little spam that you will see. But if it is getting to the third page, the spam increase.
There are mostly topics related to sports that are being ignored by the mods and all of them are spam. It is a possibility that the admin of the forum does not want the mods to take care of those threads as they are being spammed by gambling signature participants. It should be the job of the BM to restrict such spamming and almost all BM are happy with the outcome from a big thread which is why mods do not want to close them.