Earlier quoted context omitted.
It's more nuanced than that. Nvidia can write the drivers but releasing them without the blessing of Apple blows away any chance of them getting that sweet GPU contract back. Nvidia doesn't have much of a real world application outside of GPUs in enclosures to keep the drivers alive. The reason to keep drivers ready is the potential for a very large contract from Apple.
Word on the street is that Nvidia didn't get much value ($) out of working with Apple, so perhaps both parties aren't super interested. Same story with Nvidia and gaming consoles - last few gens of consoles have not used Nvidia chips and Nvidia doesn't see it as a big loss. The margins must be too low. Nvidia seems to aim for higher margin products these days with scientific computing/data center/deep learning/hardco…
The Nintendo Switch uses a NVIDIA Tegra, and NVIDIA put a decent amount of work into selling it - the NVIDIA Shield TV console is basically a tech demo for the thing after all.