Nvidia can’t meaningfully sign their Linux drivers. A distribution can, in theory, include Nvidia drivers in their build and sign it, but the logistics of out of tree drivers is just impossible.

Redhat toys with the concept of a whitelisted ABI for some limited range of kernels, but I’ve never seen a driver actually roll with that.

Basically Linux would need to embrace some form of ABI, and there’s been zero interest in doing so.