Wait what? I thought that's obvious. Facebook and WhatsApp don't even have the same type of social graph, multi-brand approaches are probably always strategically superior and changing the fundamental concept behind high-growth apps tends to be a high-risk endeavor.

There are probably a million more reasons not to prematurely integrate. (I guess they would also need to quit their e2e encryption in the process.)

Would there be any benefit beside convenience? Honest question.