AMD blocks partners from implementing DLSS. You're probably right that it's not paid bullshit as the payout isn't monetary. But it's still being blocked due to the partnership.
This is hardly the first game to do this. Jedi Survivor, RE4 have the same problem. AMD sponsored FSR2 only. The work required to implement FSR2 or DLSS is basically the same (motion data). That's why DLSS mods were immediately available.
Since FSR2 was released not a single AMD sponsored game has DLSS added. Even games done in engines like unreal where all the dev has to do is include the plugin.