Why is political discourse forbidden from boards discussion?

Because it just devolves into fighting and hate. Check any thread politics gets mentioned on Reddit

We actually allowed political discussion in General Discussion for a while VERY recently. There were some people who legitimately wanted to have a civil, quiet conversation. Ultimately, however, those threads still spiraled downward into arguments and fights, and so we made the call to disallow it again.

In short, it's not allowed because experimentation proved that it led to too many problems.

Because it's always off topic when discussing a video game. There's interactive media that involves politics and generally they can't be considered a game at all. There's movies like Shclinder's List, and there's movies like Happy Gilmore. League of Legends is closer to to the Gilmore side of things. It's people playing a game for fun. Keep the documentary and political intrigue side of things in it's own space. Literally, find somewhere else to talk about what you want to discuss. They are probably more receptive to it anyway.