The answer is that no one at WotC knows what D&D is supposed to be at this point, so the setting went through 20 years sailing with the Ship of Theseus, with a captain whose sole focus seemed to be fantasising about dark elf matriarchs dominating him. In the middle of that, the game's Fourth Edition came as a messianic figure from the sky in both mechanics and setting, and was fittingly crucified, continuing the ever-expanding clusterfuck generously called the Forgotten Realms.

For me the retcons aren't even the worst part. There were zero logical reasons to name that game Baldurs Gate 3. It doesn't continue the story and the mechanics are completely different. They just misused the big name, to get people hype up, and sadly, it seemed to have worked.