I think it falls under the forum rules of "off-topic discussion" which most forums established in the long-long ago.
Most forums are gonna have a thread/section for politics (and anything else that might get brought up frequently). And they don't want people going off on tangents about things that aren't related to the topic of the thread, whether that's political arguments/discussion in a video game thread, or discussion about video games in a political thread.
Politics, movies, religion, cooking, etc. are all potentially good thread topics for the "Everything Else" section.
