I would imagine that ownership of Nvidia's drivers would be more clear cut than most open source projects. Wouldn't it only be Nvidia's employees and contractors that have worked on the driver code? Then by default Nvidia would own the rights.

If Nvidia doesn't own the code, do you then imagine they're in a sort of licensing agreement with the rightsholders that allows them to distribute the binary blobs but not the code?

I don't understand what situation would lead a corporate-sponsored closed source project such as Nvidia's drivers to be in a position of complicated ownership.

AMD and Intel did it. The excuses ring hollow.