It was a UX problem, not a problem with the core concept.

Now, decades in to The Web, it's also a chicken/egg problem, because almost no sites are designed to behave OK under reasonable customization by the user, and almost no users customize their browsers' default styles, so why would sites change to accommodate that? Aside from the light/dark thing, of course, and you do see users pushing for support for that, and sites putting in effort to support it.

If Apple expands Dark Mode to include a half-dozen other options for a11y and such, I bet you'd see support for those become fairly common. It's just got to have a decent UI and the push has to come from a browser with a large enough user-base to encourage site operators to care. Once upon a time, Firefox could likely have done it, assuming they could manage not to screw it up. These days, Apple, Google, and MS are the only ones who could realistically try.

Actually, we have another version of this, now that I think about it: reader mode. People seem to really like it.