One of the Crawl design philosophies is that it should be possible to play without needing to consult a wiki. E.g. inspecting a monster shows you its spells and their damage ranges, there's a searchable in-game encyclopedia of all items/spells/monsters/etc., there's an extensive in-game manual with things like species skill aptitudes, examining an item tells you exactly what skill level you need to use it optimally, and so on. There's plenty of useful stuff on the wiki, but it's not a priority to update because it's not entirely necessary.
I mean yeah, I agree, I'm a longtime player. I appreciate DCSS's in-game discoverability. I find wikis useful for more in-depth explanation of game mechanics though. How combat rolls are calculated, etc. Ideally a wiki would provide that kind of deeper level of information, guide materials, etc.
Interestingly, DCSS's best source of info is the IRC bots/learndb.
Factorio has a similar goal, which actually works really well. It lets the wiki focus on strategies and things that aren't well described in-game, but for quick "how does this work" you can just stay in game.