I've been spending time in ancient cities and I'm wondering what the lore is around them. Was sculk a parasite? Did villagers build them? Are ancient cities related to trail ruins?
They're so intriguing to me, but I can't imagine how they got there
Game theory on YouTube has a series of videos that posit the players as being the last remaining population of a long dead race of Master builders and Craftsman that ultimately died out or fled to a different plane of existence. You should give them a watch, it adds some fun things to think about.
Personally I think pillagers had something to do with them. Some of the wooden platforms around the place use the same materials pillagers tend to build with.