So say I link a few tracks on a page. One is on archive.org, so that’s fine for everyone, hit play and off you go. One is under copyright. If the viewer has it in their library they’ve configured their browser to know about on their machine somewhere, they can play it. If they’ve bought it on bandcamp, they can play it. If they have a Spotify account, they can play it.
Don’t know if that makes sense. But I’d like to just link to a track in a webpage and have it playable in the page, regardless of where the visitor ‘owns’ it.