This. When people say "I wouldn't use this because it hasn't been updated for years", maybe it's because it doesn't need updating?

I'm not saying that I fully agree with that logic, but I think it's a pretty understandable behaviour.

A video game emulator getting an update every decade though? Some low level tool that's never changed since the beginning of time? Yeah, they're done, what's the problem.

The ground shifts under software. OSs change, dependencies get updates, engines change, compilers are improved occasionally in ways that aren't backwardly compatible. If the maintainer isn't at least checking it's not broken, and updating a changelog to say that it's still working, then you can't safely assume it's fine. "Not updated for years" is shorthand for "It could be broken, but I don't want to be the person who goes through the effort of checking."

If you want people to run your code against a set of pinned dependencies from the last time it was updated then that's one thing, but if you people to run it with an up-to-date set of dependencies on a new OS and on the latest compiler or runtime, then you can't just say it's 'done', because things can change outside of your code that means it won't work any more.

I’ve seen projects that haven’t had a release in years, but the maintainer is still answering questions. I would say that counts as actively maintained, since there’s still someone around to handle bug reports.

I'm not so sure of that. Ask anyone who's ever used VBScript, ActiveX, Flash, <blink>, <marquee>, or (soon) XSLT.

The web likes to portray itself as championing backwards-compatibility, but for better or worse, it is quick to drop technologies perceived as harmful or merely wasteful. If you're unfortunate enough to jump on the wrong bandwagon, you can easily be left behind, and any older pages left untouched can quickly become non-functional.