All these games still exist on the indie side. There are tons and tons of them. Why people need Sony specifically to do them?
If Sony Japan was still active they would 100% ignore all their output and not even count them in their list wars (like they do for GT7, MLB, Destiny and PSVR) but now they have an angle.
Lemme fake cry and make an article about it so all the haters can shit on Sony
Because with Sony they would be 1P and potentially be better games with larger budgets and more polish. And under Sony, they could more directly be used for bolstering platform variety, cost-effective transmedia initiatives, get all the sales revenue (or at least more of it) even if some were multiplat, and prevent direct competitors from shoring up those games/IP to use as foreclosure against them.
So, basically, a lot of reasons.