GPU time costs money but it's a fixed cost, doesn't matter what the GPU time is being used for, therefore it won't be per-game. The end.
For similar reasons, you’re not just going to rake in the money mining bitcoin because you bought a bunch of computers.
Or maybe to make the point even stupider, you could make a game about training neural networks same as you would on a real cloud service provider. If you can understand why google doesn’t charge a simple monthly flat fee for cloud computing of neural nets, you can understand why they can’t charge a simple monthly fee for computing neural nets in a game.