I've encountered this on both of those sites.

A Wikipedia deletionist resulted in a movie going without an article for months, despite my efforts to at least give it a stub page. The film was by no means an obscure arthouse production or anything like that, the not noteworthy objection was pure nonsense. Someone other than me eventually won that battle.

A StackOverflow deletionist deleted my question, fortunately after I got a decent answer, on the grounds that it was a duplicate of an existing question. The explanations in the answers were indeed similar, but the symptoms were quite different, especially from the point of view of someone who doesn't already know the answer. (It turned out I had made a false assumption about the way parentheses are treated in regex. Unlike in many contexts in many languages, it doesn't only affect precedence.)

For more on what's wrong with this, see gwern's "In Defense of Inclusionism" [0], an essay on this topic.

[0]: https://www.gwern.net/In-Defense-Of-Inclusionism

I would expect that to happen and be appropriate since eventually most questions will have been asked and most articles written. If you put aside information on new things in the world, those two sites are approaching a "finished" state so there's surely not much of value that anyone can add anymore. Of course, they may still be overzealous in deleting.