Windows is the de facto OS for PCs around the world. Now Xbox becomes the de facto “OS” for gaming. It’s a way to use the Xbox brand to promote gaming amongst the mainstream, who still don’t strongly associate Windows with gaming, and thus a way to grow the gaming market, which they say is stagnant.

I think the “This is an Xbox” campaign is a brilliant move from Microsoft.
They can get free marketing for Game Pass with every gaming PC, the same way they get free marketing for Microsoft 365 with every PC from any manufacturer.