Many engineers see a "chat app" and a "social network" and they don't see how they can be competitors, but they really are: they compete on being the transport of communication with your friends.

Long-running WhatsApp groups with your family or a specific group of friends is completing exactly what Facebook doesn't successfully provide and what Google+ tried to: a way for a more private discussion within different social circles. And on top of that, there are many people who resist Facebook for "privacy" and happily use WhatsApp (which is very very ironic, if you think of it).

The acquisition of WhatsApp (and Instagram) has been one of the smartest moves from the Facebook management. And not only that, they even handled it correctly afterwards, by not merging one into the other, resisting the usual technical urge for refactoring, unification, removal of duplicates.

Now they basically own all the most successful communication platforms. They own the primary way most people use to communicate with the world.

I always thought the plan was to move Parse infrastructure onto Facebook servers...

Parse was already monetizing and they could see the margins they were getting, and were not satisfied.