Why are you this comfortable? Netflix, YouTube TV, Twitch, Sling, Amazon Prime Video -- basically all streaming services offer flat rates, not per-MB ones.
Further, all existing game library services tout unlimited gaming as a primary selling point! That's the primary reason you opt into Gamefly or Nvidia Shield, at least according to their own marketing.
And this offering is not for high-end gamers. It's taking the benefits high-end gamers get for their investment into their hardware, and making it available to the millions of more casual gamers. This isn't for high-end gamers, so creating a business model for them using Stadia makes no sense.
Finally, you're not thinking of this at the right layer if you're thinking in terms of things like s3, ec2, lambda, etc.. This is the product that's built on top of those, and the single price problem has been present for hundreds of years. It's a solved one, just ask any current MMO or hell, any clothing manufacturer. You're basically saying that an XL t-shirt is going to cost the same as a S t-shirt, despite tens of thousands of examples to the contrary.
YouTube (and Google Play TV & Movies, which appears to carry the same for-sale/rent content in a different storefront) and Amazon Video also both offer purchase of individual content items as well as a common flat rate subscription to certain content.
I don't agree. Anything is scalable.
This does benefit from economies of scale, but it’s not something you can just solve with infrastructure and fixed cost. No matter how many computers you have, you’re still going to do multiple orders of magnitude more calculations to render high end games than stream a song. And you’re going to deal with difficult load balances because every twelve year old gets home from school at the same time (exaggeration but point stands). GPU time costs money.
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.