I think that's because the service is hosting the data, not the data itself. Holding onto the data which you (expect to) own is pretty much akin to a person tak

I think that's because the service is hosting the data, not the data itself. Holding onto the data which you (expect to) own is pretty much akin to a person taking care of a pet for money and when the money is not paid, keeps the cat. It's the obvious solution - the cat-sitter doesn't have any other leverage here - but Github does have other options than holding onto the cat.