I suspect it's more about the timing of the deals and the business side of things, moreso than the product side.
We already know that the Nuro + Uber + Lucid deal was struck in part b/c of the PIF connections across all these companies, and in many ways is also a partnership of convenience on all sides. It gives Lucid a story about autonomy that they probably wouldn't be able to achieve on their own; Uber gets a Waymo/Tesla-like vehicle to work with (without themselves having to build it, not even clear they'd own these cars), and Nuro also doesn't have to build anything and has some say over the car's hardware.
The Nvidia deal feels more like tying themselves to the latest tech, getting some press and attention, and possibly giving themselves a longer hardware roadmap. In the past ~10 years ever since autonomy really started to be an active part of car tech, every car promises to have "all the hardware needed to be fully autonomous" only to take it back 3 years later. I suspect the Gravity will fall into the same camp.