make it easier on their server side to authenticate purchases and then to use the same PSN account systems to matchmaker for easier cross-play.
Like fraud prevention?
Easier cross play?
I mean yeah this is especially true for online games as this is a form of DRM for Sony and it gives them control to easily reject or accept keys and ban users using their pre-existing systems.
Same thing with cross-play, it’s possible that some of these games were designed to use PSN systems and so that makes integration easy. No clue, but if true it makes sense from Sonys perspective on both of those fronts.