The core books.emphasize the DIY angle pretty firmly, and actually if you look at Seyting books like Ravnica and Theros that depart from standard expectations heavily I'd say that WotC provides templates for how to depart from D&D norms at the same time that they provide a big picture to use at will.This actually gets to why I was asking the question in the first place. (I even had Star Wars, specifically, running through my mind at the time.)
Personally, I've always looked at D&D as a toolkit, as well as a broad genre unto itself. The official settings have always been nice conveniences for me to yoink inspiration from, but I've almost never really paid attention to the deeper lore, read only a handful of the books, didn't play the video games, etc, etc. So to me, D&D really isn't a place and a cast of NPCs; it's only a set of rules.
In recent years, I've sensed a push to codify the settings within the rules themselves, though maybe I'm wrong about that? It makes it marginally harder to "play D&D" in the manner of playing with Legos that happen to have some Star Wars pieces mixed in, and biases toward the manner of playing a specifically Star Wars game.
As a habitual game DIYer who started in the early 80s, it's not a huge deal for me, as I can just ignore and integrate as I desire. But it does make me wonder if it makes it more difficult to get new players interested in homebrewing worlds when they might be expecting certain things of D&D. ("What?? There is no 'Shangri La' on the map in the book! And what do you mean trolls are short? And not flammable??")
So it's really great to hear from people new to the hobby, like @King Babar , who's going all iconoclastic and building their own stuff. I'm glad the DIY ethos is alive and well, and I really hope that proves to hold for more casual gamers, too, as the hobby attracts more people.