Long story short even though you seem to be without a past, or with out ambition, D&D is about theatre of the mind at times. They can be who you want them to be
Sure, that's true, but there's an issue of narrative framing.
Other RPGs don't tell you a lot about your past. Pillars of Eternity, for instance. The original Fallout tells you where you're from, but nothing more than that, and New Vegas tells you what you did for a living at the start of the game and the particular assignment you were on, but that's it. The Outer Worlds gives you tongue-in-cheek options for your background that may not even be meant as cannonical, and otherwise tells you nothing. Arcanum lets you pick from a list of backgrounds (and you can opt to have none), but otherwise tells you only that you were using a particular transportation at a particular time.
The thing is, all these games, the story is presented in such a way that clearly situates you in it, and makes you (at least from your perspective) the center of that story. It's your
In another thread, people were pointing out how all the companions were special, and your PC is just an empty slate. The thing is, I think, that in those other games, companions have their own stories, sure, and you have yours, which just so happens to be the main story of the game. That's your story, not theirs. In BG3, however, you share that with all your companions, plus a bunch of other people.