Nvidia is opening their source code because they moved most of their source code to the binary blob they're loading. That's why they never made an open source Nvidia driver for Pascal or earlier, where the hardware wasn't set up to use their giant binary blobs.

It's like running Windows in a VM and calling it an open source Windows system. The bootstrapping code is all open, but the code that's actually being executed is hidden away.

Intel has the same problem AMD has: everything is written for CUDA or other brand-specific APIs. Everything needs wrappers and workarounds to run before you can even start to compare performance.