Given that federated services always seem to coalesce around a provider that the bulk of people use, federation becomes a sort of implicit threat. Nobody really wants to run their own servers, but they know that it might be possible if their current host does something egregious enough to make it worth the effort.
The implicit threat of federation
In a federated architecture, most users tend to coalesce around one provider. Few actually want to run their own server, but the fact that that option exists, acts as an implicit threat which keeps the current host honest.