Google, OnLive, Gaikai, Apple

None of whom actually made games, just let you stream other companies games. Microsoft will absolutely let others stream their games if they wanted to.

Then why is Starfield exclusive? Why are there still a plethora of console exclusive games?

Starfield isn't a cashcow that makes more and more money the more people that play it like GaaS games like COD are.

No, I’m just accurately assessing that there are a very finite number of game studios making games at the scale of AB.

Activision Blizzard realistically only make 3 games these days - COD, Diablo, Overwatch.