I'm not sure I understand the motivation. Seems like they don't have much to gain and they do have a lot to lose.

While (anecdotally) Facebook doesn't appear to be very hype with the youth today, Instagram and WhatsApp still appear to be quite popular. In a weird way Facebook is both the mainstream choice and the underdog, that's a good position to be in IMO.

Beyond that what does it mean for people like me who use WhatsApp but do not have a Facebook account? Is the plan to force people like me to create a Facebook profile?