Why is that surprising? A compressed video stream is obviously smaller than actual textures and mesh data of the entire planet. You can’t compare the two.

Also NVidia doesn’t produce the stream out of thin air. They are running the game on their own servers then compress the final image and send it to you over the net. While MS sends you the actual game data like meshes and textures and you compute the screen image on your own machine. It’s not the same. What Nvidia is doing is expensive since for every client that connects they need a graphics card, a cpu and a SSD running in a server farm. If MS would do it that way you have to pay a subscription fee to play Flight Simulator. What MS does is just sending files. Since bandwidth is obviously exponentially cheaper than spinning up an instance of the game on a server for every customer they’ve decided to do it this way. So you only have to pay once.