Because, like most of the population in the West, HN readers are not actually liberals but rather centrists, which means they lean roughly equally conservative, liberal and socialist on the political triangle - on average.

Sometimes you have to trade personal liberties (makes liberals sad) and/or privileges (makes conservatives sad) to obtain better societal outcomes, i.e. mandatory vaccination or minimum wage. Those are socialist policies.

And since the major media and thus our shared social space is heavily anti-socialist (qui bono?), everyone is closeted and tries extremely hard to justify socialist policies as liberalism, which is not shunned. Hence people in the US now perceive them as closer or even "allied".