Short answer: Because oftentimes a thread about a technology is about its concrete operational characteristics and applications, not it's social effects.
When you start dragging those into the topic, there's shockingly little depth to probe. AI will automate people out of jobs eventually - okay, and? You've moved the thread off topic. I came to read about how OpenAI works, not what the left, right, center, and upside-down think about the larger concept of AI, rather than the specific implementation called out in the thread title.
Here's the thread I was talking about: https://news.ycombinator.com/item?id=13103742
A cursory reading suggests that somehow, that particular rabbit hole was avoided by everyone there. This kind of goes into what dang was saying, broaching the topic you just did in that thread would have just been unwelcome noise.
Do we really to relitigate "what about the jobs?" any time an AI or deep learning framework comes up? Is that really an interesting discussion to have in every thread?
That said, sure, not every thread should re-hash the same conversation, but that's neither exclusive to politics (see the discussions in every thread about JS frameworks) nor is it the problem being called out by the moderator.
Again. Do we really to relitigate "what about the jobs?" any time an AI or deep learning framework comes up? What if there are sites that are not Hacker News that are better for that kind of discussion?
As for other sites, no, absolutely not. Politics is unavoidable. You can enforce a silent acceptance of the status quo, but that's in itself a strong political (reactionary) position.
These two views are mutually exclusive. Either technology discussion can be separated from politics discussion (and given the other thread, we have evidence that it can), or it can not.
You're telling me that I can't discuss a topic without touching this other topic, and yet here that is happening right in front of us.
There are times and places to have political discussions - the fact that I do not engage with my mom on political topics over Thanksgiving turkey does not mean I am not interested in politics, it means I am not interested in politics in that particular context.
Mostly because I know that the discussion will end in anger, hurt feelings, and not a single changed mind. It has happened enough on this board that people, myself included, start getting very flag-happy when they get a whiff of partisanship in the air.
I especially do not appreciate the implication that not wanting to have the discussion "here" is a political statement of anything other than wanting to avoid a headache. I must point out that insisting that X be talked about when someone has expressed disinterest in the topic is hard to interpret in any way other than hostile disregard.