I've been using WhatsApp since 2016 when a Detroit friend of mine from Lebanon wanted me to join a group chat with some of his friends, not all of whom were in the US with us.
I stayed with WhatsApp because I have a few overseas friends who find it the default messaging app.
I use it a lot now in my capacity as the publisher of Prism & Pen on Medium. Many of our writers are from the UK, Ireland, Australia, South Africa, India, and even Germany.
For them, text messaging almost defaults to meaning "using WhatsApp."
I really wish it were more standard in the United States, because it sure would make things nicer and easier.