No doubt because most large web corporations have completely switched to javascript for their anchors (ie, #) and no longer use HTML spec anchors that actually work. I'm looking at you Microsoft Github.
Where don't anchors work when javascript is disabled? (With admittedly very brief testing just now, I couldn't find any such cases.)
I just went to the most recent github tab in my browser session and found one instantly: https://github.com/quiet/quiet#dependencies
That said, the github one is a sort of interesting case, insofar as they're doing it to avoid user-generated content clashing with their page-chrome ids... while still preserving a readable URI that matches what the content creator expects. Which doesn't seem like an unreasonable case, to me.
You'll note that there is a real anchor on that link -- https://github.com/quiet/quiet#user-content-dependencies -- which works without Javascript. It's just rather inaccessible.
I had tested linking to specific comments in issue threads, which does work with JS disabled (unless I've completely messed up...), and assumed that linking to parts of documents, as less complex/application-y would obviously work, but as you've pointed out it doesn't.
That's highly disappointing.