The majority of Desktop browsers support extensions that provide support for dark mode. On mobile I know Android Chrome (via chrome://flags) and Firefox (via extensions) support dark mode. Don't know about Safari and other mobile browsers but I feel that overall there are plenty of options for dark mode on HN without a separate site specific implementation.

I also have noticed that I never use the site specific Dark mode implementations as it is a lot more convenient to globally enable dark mode (at night) rather than playing around with toggles for every website that supports it.