This is why AMD has built their upgradable FSR API, so they can override games with drivers to use the newest versions of FSR.
The problem with other games is that developers do not like drivers messing around with their code. Using the FSR API and newer versions of FSR basically act as consent for AMD driver upgrades.
Another thing is that messing with versions of FSR in games in other ways can become really messy after a new game update is released. If AMD needs to do custom workarounds for certain games, those workarounds may break games after updates. With the FSR 3.1/FSR 4 upgradable API, this should not be a problem moving forward.