You're forgetting that's the game has coop, and if you're playing coop with 3 friends, you would be forced out of any companions' stories without Origins. So first of all Origins are allowing you to experience that content in coop. Plus in single-player there are certain moments in companions' stories which you're not allowed to see, but when that's your Origin you get all the details. And after all there are players who would prefer to play a character with more ties to the world above a character with more player agency for the backstory and tags.
huh, i guess i'm different. If I was going to play a D&D game with buddies, for sure we would all be rolling our own characters. It would feel so disconnected to be playing a premade character. I'd be curious what Larian's famous statistics say about how many people played as origin characters vs custom made characters and multiplayer origin vs custom players.