Because the nvidia binary driver never crashes, works every time, including with prime, and has never ever had a security problem.
I do not promote Free Software out of Closed Source software being Evil, I promot Open Source software because there is the possibility that you yourself can audit the code or hire someone to audit the code. That way you know that the DRM-protection you just bought for your videos was not just something where the first bits where bit-shifted with the text RANDOM_STRING. And that your random generator truly is random. And that your application really uses SSL in a secure fashion, and not in a way that you information can be decrypted in predictable ways.
Yeah, I am an CS, and have a lot of friends working for businesses only to audit code.