I think the point is that places exist for jokes that don't add anything, so we can just go do that there, rather than changing the definition of what this is

Nowhere in the guidelines [0] does it say "do not post jokes that don't add anything". It does, however, say:

    Please don't post comments saying that HN is turning into Reddit.

[0] https://news.ycombinator.com/newsguidelines.html