why would nvidia not create their own foundational model?

Why didn't the people selling shovels to gold miners dig for gold themselves?

Because Nvidia is making actual profit selling hardware to those who do, not hoping for a big payout sometime in the future. Different risk/reward model, different goals.

They are printing money right now, and their customers are taking all the risk. Just keep delivering and enjoy success.

They have a bunch of Nemotron models. They can make more money from five(?) competing frontier labs than from trying to monopolize the frontier themselves.

Why doesn't Apple make their own iPhones instead of contracting them to Foxconn?

Comparative advantage.