That logic checks, but it only makes sense if you come as an Xbox owner. People who owns PS4 has very little reason to consider an Xbox Series X even from the 'upgrade PC-like' mindset.
I guess that's enough for launch since there's plenty of Xbox owners that might be interested on this as an upgrade and availability is definetly not there now to worry about expanding it to new users.
It's a personal choice, nothing that set in stone as you propose. I'm going from PS4 to Xbox series X.