It’s really more for the convenience of getting your games from a web browser.
Exactly, it’s a niche service that only appeals to a fraction of the folks who play games, but it also requires the operator to purchase servers with graphics cards and set them up in datacenters near everyone who has an account in order to minimize latency. It’s not viable for people who have slow internet or live in a rural area, especially when so much of their income goes to licensing game titles for use in the service.