Thing is, most people want to listen to copyrighted music. Federating copyrighted music is a surefire lawsuit for anyone who hosts that federated service.

And you don’t need federation for acquiring music files. Torrents are better for resilience than federation, since they form a distributed network, not just a decentralized network.

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There is a piece of software that implements federation for music, called Funkwhale.

This is their flagship instance: open.audio
That flagship instance hosts basically only Creative Commons music and podcasts, due to aforementioned problem.
The other instances I’ve seen federating with it, were generally self-hosted by musicians or podcasters to share their own work.

I imagine, if an instance started federating copyrighted music (which wasn’t either separately licensed by the artist), it would need to be defederated by everyone else in the network ASAP, to avoid lawsuits.