https://www.meta-chart.com/share/how-wikipedia-deletionism-w...
Two important takeaways are: A lot of stuff on Wikipedia just isn't encyclopedic. For example, there's a lot of sports trivia about obscure teams and local leagues. Such data deserves structured storage and not Wikipedia, and I just don't feel "2013 Richmond Raiders season" is more important than any single matematician who worked with Erdős.
Second takeaway, a whole world of topics is just not ever noted by Wikipedia. For examples, you can have whole branches of local music scenes ineligible for note because every single artist fails to "be mentioned in a paper made of paper" (in 2010s, seriously) or "sell 3k discs made of plastic and foil" (again, this is in 2010s).
If there's some kind of consistent policy I definitely don't see the value of it.