Data security is a huge issue, Facebook.com has very specific whitelisted access patterns encoded as CRUD endpoints. 1) Users want to make sure their data is used in non-creepy or non-stalky ways; 2) Facebook's business needs to control the access point so they can serve you adds or otherwise monetize. So the API exposes only limited access patterns, the API TOS disallows caching, and they go to great lengths to prevent scrapers.

If immutable fact/datom streams with idealized cache infrastructure becomes a thing (and architecturally i hope it does) it's going to need DRM to be accepted by both users and businesses.