I would argue that the games you purchased (and thus own), and the cloud service Luna offered are two separate things. It is much more difficult to argue that you somehow “own” the hardware of a cloud gaming service than you do the licence of a game you bought.

Amazon is under no real obligation to perpetually offer their cloud service. You are effectively renting server space, and they can stop offering that at any time as long as it is in line with the service agreement.

This is also why I prefer to own my own hardware, and not rely on cloud services. After you purchase hardware it will always be yours.