So is this liability reduction for them? Too many subpoenas and this makes responding to them more efficient? It doesn't seem like "messenger is e2e encrypted" actually matters for marketing and adoption so either it is a cheap fiction for marketing or there is a motive I don't understand.
#2 is interesting. I am very curious what the ultimate plan for having 2 messaging apps is (at least in Zuck’s head). My bet is that his fantasy is to eventually merge them into a single service: Meta Messenger.
They could do this very gradually. First rename WhatsApp to Meta Messenger. Keep everything else the same. Then with interop being implemented slowly merge FB messenger into Meta Messenger.