The non-free features for the Nvidia cards and many other chips are achieved by the card itself running closed source binaries. It is actually probably a better way to protect IP anyway since no one can decompile the encrypted binary (well until recently...).

Open source and proprietary software exist as a duality. It's not an absolute expectation that everything will be open source but Nvidia is very late vs its competitors.

Google, Windows, macOS, etc. all have large open source parts. Games are kind of an exception because they are treated like a single work of art. Also, crucially no other software or hardware has a game as a dependency so interoperability isn't a concern.