Sony can’t just decide solely at their digression which games require PSN integration and which ones don’t. That is a joint decision between the developer of the game and Sony.
Sony can’t just walk into Coffe Stains office for example and demand all players of Goat Simulator now require a PSN account; Coffee Stain would have to decide to agree to that.
Arrowhead didn’t have to agree to it, but they did. Now they have to deal with the consequences of that decision.