The latter sounds like the smarter move, so it's probably the former.

One of the many reasons is likely to make sure models stay specifically optimized for NVidia hardware, by floating them to the top of the search results and making sure that they're the only ones that get special prices on the tools and hosting. It's such a fast-moving industry that they know they won't always have the fastest chips indefinitely.

To stop a competitor from getting the same kind of control. Particularly if its one of the foreign (to US) ones that's less amenable to whatever US policy is on any given day.