That was kind of obvious from Zuckerberg's statement. It's all about messaging privacy. All this is to push for Federal preemption of California's new privacy law, which takes effect January 1, 2020, and is a lot like the GPDR. Facebook is screwed if that takes effect.
*when that takes effect
It still baffles me that people don't realize Facebook messaging is unencrypted... How can you wonder why Facebook knows that you want to buy puppy pampers if you have been messaging your friend Karen about it all day.
Few people care. Skype was end to end encrypted before Microsoft bought it.