Email has MIME, there are calendar information formats (ical, IIRC), and various MIME handlers. The primary block was that Microsoft owned the corporate desktop, and competitors, until Google came along, couldn't agree on interoperable standards.
Facebook and Google win by being Web based and "in the cloud". Facebook had its social graph, Google had the fact that many users were relying on it for email, and increasingly, companies are.
There are any number of other problems surrounding mail, with privacy, spam, true federation (spam means residential/consumer IP space is virtually always blocked), and access from multiple devices being prime among them. Diaspora is interesting (I'm on it and active), but very small and growing slowly if at all. I do very much hope that some federated system (Diaspora, Friendica, FreedomBox, Sandstorm.io) will emerge, but it's a long and slow process.