ISPs also "facilitate the creation and routing of content". We just don't think of them that way because they exist at a lower layer and we don't directly interact with them. Instead, services like Facebook use the services ISPs provide.

Thats some pretty contorted reasoning. ISPs only carry content after it has been created and they do not route traffic based on it's data payload, only it's addressing metadata set by the sender. The protocols they implement were specifically designed not to care about the data payload and just do what the sender told them to do regarding addressing and delivery. Internet users rely on them to do what they are supposed to do, as clearly laid down in the protocol specifications.

Various social networks use 'relevance' metrics, keywords in the text, timeliness and all sorts of criteria to choose how to distribute or sort and highlight content and they change these algorithms over time. They are part of the value the service provides and clearly their responsibility.