Whatsapp is such a big cultural force that many of my non technical friends and family members refuse to use anything else. No mail for full res photos is one thing, but you can't make them use anything else. Everything lives in Whatsapp. Todos, notes, reminders, sharing stuff (airdrop is the only exception if everyone involved has iOS). It is less because of whatsapp features (Nobody uses any features like payments), and more because of the simplicity and ease of use.