HN is very American, and somewhat half of America is pro-Trump (which often comes with being anti vaccine to some extent though they don't necessarily see it like this), is how I see it. I was quite surprised at first too.

Large cities are much more on the Democrat side and developers tend to live in those so the number of Trump supporters is still on the lower end.

It’s not about being American, it’s that having a brain so cooked as to believe in total conspiracy theories AND being a HN regular/developer used to be mutually exclusive.

HN has just become reddit for tech, and as tech became more accessible, the conservation population of tech workers and hobbyists did too.

The other part of the answer is compartmentalization, I guess.