Exactly 10 out of 10 moments big money is involved, everything goes downhill. I'm not saying they'll just stop updating BG3, they are just likely hellbent on Karlach's garbage ending because they can go for DLC that way, just like Bethesda did with Broken Steel for Fallout 3. Like, back then we still had obvious solution to the quest that didn't require anyone to "sacrifice" and couldn't use that. Same thing here, who cares that there are like 20 obvious ways to save Karlach, Avernus DLC is what sells so you'll go there. Track record doesn't mean a anything these days
Perhaps I’m just in a very depressed mood today, but I think that they are unlikely to plan to continue the story of Karlach even in the DLC. I mean the game is already selling great, even with Act 3 looking like it's still in early access.