Why sell software and hardware once when you can sell software, the hardware it's hosted on, and the support and services to manage that software and hardware every single month. It's why companies like Adobe and Microsoft have tried to push their main, relatively static[1] software packages like Office and Creative Suite over to a rent-seeking model. And it's why selling cloud services is all the rage.
It's not a good way to do things, it's not good for any consumer or user of those things, but it prints money on a stable and continuous basis in perpetuity, because people lose everything they paid for when they stop paying.
That's why cloud gaming is going to keep coming up year after year, no matter how impractical or stupid it is.
[1] For the vast majority of users, the difference between any given version of Office or Creative Suite and one released five or six years prior is nearly zero. Almost nobody needs to continually buy these.