You've almost got it, except:
> Wikipedia has a bunch of languages that were used by like one person, because there is published material on them
No. It's more like, there are plenty of articles on Wikipedia that don't meet Wikipedia's notability guidelines AT ALL, but when you write an article on Wikipedia and enough time passes without anyone noticing that the article is poorly sourced, then eventually the tendency of Wikipedia community is to just keep it.
This is what has led to the what-about-ism regarding Odin's deletion - there are lots of other programming languages that also don't meet the notability guidelines, yet, to this day, still have Wikipedia articles.
Could someone come along and propose deletion for such articles? Yes, of course. You yourself could go do that right now, if you want. But nobody's getting paid for such work, so someone has to want to. The tendency of Wikipedia editors is that, when an article is many years old, they would rather flag it for improvement rather than simply throw away years of fellow editors' work. Whereas an article that's brand new is likely to not have much work put into it, and also more likely to be self-promotion and/or spam.
This is very frustrating for people who create Wikipedia articles and have them deleted. "You mean, whether or not my non-notable article gets deleted or not is just the luck of whether someone comes along and notices that it's not notable?" Yep. Like I said, nobody's getting paid for deletion work.