Mods do as they see fit without notice, recourse, or the need to answer to anyone. There is no real hierarchy or standards or oversight.
At least that was the gist of an explanation a while ago from "powers that be"
Either you live with it or not.
That being said, there are usually different mods for different forum areas. I avoid posting in one area and even removed it from my forum list because the mod in that particular area is...well, let's just say accuracy and the safety of advice given to fellow members is of little concern to him.
Most of the mods do quite an amazing job of keeping things under control.
Bottom line: If you don't like how a particular mod handles his or her playground, just get out of his sandbox ;)
Disclaimer: I don't know the particular thread or any details that may be referred to by the OP, this is generally speaking only.