User are encouraged to flag content the judge off-topic. And the definition of off-topic is quite broad:

On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.

Probably people don't find their intellectual curiosity gratified by the umpteenth post about Trump. Also consider that many users are not American.