Can't speak for any country but my own (Brazil)

The reason WhatsApp is such a thing here is an interesting little historical path.

See, texting never really took off here in Brazil. Because phone service providers would charge per individual message. And while the charge was like 5 cents per message, that shit builds up. So unless you're rich... You won't be texting.

So when smartphones, and with them, data plans (that offered very little data, around 4 gigs is the average nowadays, it was a few megs back then) came around, internet-based messaging services became our texting. Because if you have, idk, 512 megs of data in your plan, that's not a lot but it is more than enough for messaging over an app.

WhatsApp was the one that got popular, no idea why.

It was popular with the youths(tm) first in the early 10s, then families hopped on, dragged in by their young-adult kids no doubt, and then... Everything! Because once the Boomers had learned how to use this one app, every business under the sun realised it could serve their purposes as well. And eventually... So did the government.

You want to order pizza? WhatsApp. Want to contact a government agency? WhatsApp. Want to schedule a doctor's appointment? WhatsApp.

Now, I got my friends and family on Telegram, largely because Telegram has nicer features (still closed source though grumble grumble) but I still need WhatsApp for work. It's how I talk to everyone: The team, the boss, the contacts, etc.