I'm not sure why you think that. Hacker News is amazingly conservative, not in the "God and guns" sense, but in the "please don't change anything ever" sense. I'm not even going to pretend that doesn't apply to me, too. Hate crypto, short AI hype, can't stand Electron apps, refuse to touch anything written in JavaScript, wish code would get out of my damn browser and into compiled executables I can keep on my local filesystem. We're basically all old men yelling at clouds here.
Reflexively, this sounds like a stupid law to me, but unless the LA Times is just lying, it sounds like it's been successful and similar policies are now being pushed privately, apparently by Nasdaq, Goldman Sachs, BlackRock, and even the U.S. Chamber of Commerce is behind an effort to do something similar but without actual punishment.
It's probably illegal, though, and seems destined to eventually be struck down whenever it gets to the Supreme Court.
I also share your surprise that all white-male boards were even common before this. Mostly white-male boards I expected, but not 100%, at least for publicly traded large companies. Anybody trying to say that was meritocracy is fooling themselves. There is no way in hell there is that much of a skew in merit across gender and race boundaries.
At the same time, I very much agree with the other comments saying this is focusing on exactly the wrong kind of progressivism. It feels like George Bush putting together the most ethnically diverse cabinet of all-time, but they were still uniformly war hawks, liars, and authoritarians. Making the 0.00001% of the world allowed to have power more diverse doesn't change that power is still way too centralized. It's fine for the extreme upper echelon of women and ethnic minorities but does nothing for the vast masses of actually underprivileged people.