Streams don't have the ability to configure rules currently, so the only place they could list rules would be the stream description. There isn't that much room in the description and they might not want to pollute it with a big list. We'll add configuration at some point though.
Frankly speaking though, there is an unwritten rule in most of human society which is basically "stfu about your politics unless I've established explicitly that I want to hear about them". It's generally the most controversial subject out there and can start fights, so it shouldn't be a surprise that many or most communities would by default not want politics.
