They can totally fit Nvidia GPUs, just not particularly high performance ones. It's not that hard to find a thin-and-light laptop with a low powered discrete Nvidia GPU.

Heck, even the Switch technically has an Nvidia GPU.

Largely true, though...

https://www.asus.com/us/site/gaming/rog/gaming-laptops/flow-...

It's a very small laptop with the option to utilize a current generation Nvidia GPU.

Well, even if they could, battery life…