nVidia is dropping support for 32-bit CUDA to finish the move to a 64-bit only world/ecosystem. (Only took 20+ years)
32bit PhysX piggybacked off 32-bit CUDA, hence why it also got the cut.
I don't know why nVidia just didn't implement a compatibility layer to translate 32bit operations to 64bit, but I digress, I am sure modders will make it instead.
--::{PC Gaming Master Race}::--