The 100GB of game data I have to wait around to download.
The 100GB of streamed frames happen while I'm playing so I don't care.
This benefit is for those who value their time highly and want something to 'just work' without having to bother with installing stuff, updating, buying and setting up new hardware every year, etc.
Imagine you only have 30 mins a month to do gaming... Like many busy adults... With a PS4 or PC, you'd spend most of your 30 mins waiting for updates to complete.