A lot of people don't consider the future even when writing helpful posts. I'm as guilty as anyone.

If you link the correct answer, the person finding your post in 6 years better hope the link is still good. That's the legitimate reason scholarly papers needs to cite specific book editions and journal page numbers instead of using hyperlinks in a bibliography.

If a copy of the book or journal can ba tracked down, the citation will still work.

It's also why online-only published journals are still often formatted like a book with static pages instead of websites. If you find a journal article that's important, you'll likely still be able to find an achived copy in PDF somewhere even if the journal stops publishing or they change domains or whatever.