They made FSR vendor-agnostic for reasons that turned out to be irrelevant in the long run. It was just couple of years ago when games supported DLSS only and engines weren’t ready for plugging multiple different upscaling solutions. Nvidia and AMD tried to get exclusivity deals and things seemed fire for a moment. AMD hoped FSR would be enough for smaller players to adopt it but being vendor-agnostic handicapped them so much that everyone developed their own solution anyway (PSSR, XeSS). Not that it really matters that much because in the end modern AA gives similar results to old FSR and game devs will use what works best.