They are the dominant player in this market, I simply can't understand why they didn't crewed it already.

I can only speculate: it's because WhatsApp is giving them an always-updated social graph of a billion people right now (including inferred information on people who, like me, didn't install the application but whose numbers are in the contacts books of people who did it) and crossing this information with FB data brings more revenue than anything they can do with WhatsApp itself.

They have enabled E2E encryption, so I'm willing to give them the benefit of the doubt that they won't screw it up like they have everything else.