But these synergise—we all know that scene and P2P film releases percolate from private sites to public ones, for instance. Torrents may die in the public sphere before being reseeded from an obscure, yet shielded and resilient, private archive (I have done this). The economies of private sites encourage the contribution of new content, which after a requisite delay is disseminated outwards to the public sphere. Light is the left hand of darkness, darkness the right hand of light. (The same model applies among private sites too as content is cross-uploaded, building resilience in the shadow archive. When one private or public site shuts down, that content doesn’t all have to disappear.)

I would actually argue that where public materials are less available, it’s less because of the private sites (which will always exist) being private and more because there are no public sites for that media type to be mirrored to. Think Libgen, which absorbs almost all contributions to private book sites eventually. Music enjoyers aren’t so lucky usually, which I think is because of the language gap between the major public music site that you mentioned and private music sites which are predominantly English-language.