Idk if the GitHub analogy really works for music.

With software, the code is a tool. And you can give the code away and still make money on hosting, support, enterprise sales, consulting, recruiting, whatever.

With music, the stem is the product.

If the drum loop is mediocre, nobody cares. If it's actually good, the creator usually wants ownership, licensing, royalties, exclusivity, or at minimum, attribution. But even at that level, it's trivial. Once you remove the triviality of it, it becomes art, which is the product.

People absolutely want cloud collaboration though. Shared sessions, async recording, version history, stem exchange, all of that makes sense.

But public forks of high quality musical material don't really compound the way software tools do. Most musicians are not trying to maximize downstream reuse of their riffs by strangers on the internet.