From my estimations they could not release Episode 3 as public hype eclipsed anything any game studio could produce. The anticipation became too strong as people expect nothing less than perfection. They used Alyx to re-anchor expectations

Edit: I believe a similar phenomenon occurred with Disney's Star Wars Sequel Trilogy, objectively some mistakes were made, but the sheer outcry from fans is an order of magnitude stronger than the mistakes made, imo this is caused from the mismatch of the idea of what Star Wars can be/means to you versus what you can concretely produce (with technical and cultural constraints)