Never said that. But they should be building legacy studios with new internally made IP's not relying on paid exclusives to be where we get new IP's.
Sony has a bunch of studios working on New projects that they own. And to your other question, why should anyone need an xbox when most of those are PC as well? And if they're was any kind of agreement, who says they wont come to another platform at a later date.
You know how stupid this sounds?
It's like me saying why should anyone buy multiplatform games on ps4 instead of PC (CoD . GTA etc).
You don't buy a console just for exclusives otherwise ps4 would be dead by now same goes for xbox.