Nvidia have always shipped closed-source drivers, despite AMD and Intel providing open source drivers for their GPUs. This made the experience on Linux second class to Windows, where while also closed source, at least you knew that bugs would probably get fixed. Various non-core features simply wouldn't have support on Linux, e.g. Optimus. Also, shipping closed source binaries would limit which kernel you could run to supported versions.

Lastly, of course, this opens the way to non-Linux OSes receiving support as well.

If you just search the web for "Nvidia issues Linux" you'll see quite a few complaints. Particularly from people who have obscure configurations -- they pretty much had no chance of getting anything to work.