Amazon Prime, like many services, is a DRM hell. It won’t go to over 480p on Firefox on Linux at my end. However, instead of a rant, I am interested in why this is happening. Say, I rented the same film from YouTube Movies(Yes, such a service exists) and the quality can toggle all the upto 1080p but the same title on Prime Video is stuck at 480p. Is it because both services use two DIFFERENT kinds of DRM?
DRM is one potential reason, but not the only one.
Content is licensed under specific conditions, resolution, audio tracks, closed captions, etc. Two organisations might have licensed the same title, but not the same conditions.
You can see this clearly during the Olympics where some channels only have secondary rights, or only certain events, but only free to air, not online, etc.
Added to that are marketing and exclusively deals and in the end it’s anyone’s guess what you actually end up with.