When a person reads content that is more attuned to their political 'norms', it tends not to register as political information at all. When they come across opposing views, it creates friction, gets stronger attention, and becomes memorable. It can lead to the perception that "HN is extremely X biased" in either direction, based on who you ask.

Everything is political. It is impossible for it to not be. But it is easy to forget that when someone is espousing similar views, then the politics is just background noise and tuned out.