Blockchain solves the double spend and ownership problems, but it does requires (a) that you be connected to the internet to establish or transfer ownership, and (b) that any consumer of encrypted data respect the blockchain state as well. If I have a video player and I give it a video that I downloaded with an ownership token, that player needs to either confirm that the token is still valid and deny the ability to play the video (even though it could), or it has to get a decryption key of some sort from the blockchain and use that to play the video, and further guarantee that said decryption key cannot be saved or copied.

Blockchain does not solve this problem.