For the longest time, it was 6, then 8, and it stayed on 8 for years. Iirc 1.17 was a jump to Java 16 after a lot of internal reworking, and I guess with Java 17 being LTS, thats why they've moved to that.
Correct me if I'm wrong, but isn't the first favored by pay-to-win servers and pvp specializing servers, while 1.12.2 is favored for modding? Both seem pretty niche to me, albeit noisy niches. There have been several substantial updates to the game since 1.12 and I'm quite sure most players are presently on 1.18 or at least 1.17. And I don't have much sympathy for the plight of those P2W servers.
The lack of a 64 bit JDK build was the big blocker a couple years ago. Haven't checked back to see if Raspbian or anyone else got around to it.
I can second that modules were a way bigger deal than people here seem to be willing to admit to. I avoided 9+ like the plague because redefining one of your base visibility modifiers and the inevitable charlie-foxtrot that would entail, plus Oracles license shenanigans was just not something I was willing to wade through.