You hold a physical artifact on which some data can be extracted and interpreted by a device build for that purpose, but the legality of you playing the data is

You hold a physical artifact on which some data can be extracted and interpreted by a device build for that purpose, but the legality of you playing the data isn't implicitly tied up to the ownership of the artifact holding the data. That is what the licensing scheme is. The common assumption is to think that because you hold the storage, you are therefore entitled to decode the data held on it, but the laws about IP are there to limit this and allow to extract value from you using the device. Otherwise, you could just legally extract the bits downloaded onto your computer and keep the music files you have just streamed from Spotify or any equivalent service.