The US is one country, and what happens there is not representative of the rest of the world.
We were using whatsapp before iPhone even came to my home country, and living in Ireland now, everyone seems to be using it here as well. In fact, I'll venture as far as saying /not/ having WhatsApp is considered weird and you will no doubt exclude yourself from a lot of spcial circles.
A big part of Apple's appeal outside of tech circles is exclusivity. When people talk about premium whatever, more often than not it just means "what the plebs don't have". From that perspective, performative exclusion of oneself from some circles can be seen as a feature and not a bug. Nor is this US-specific - iPhone is even more of a luxury status symbol in much of Asia.
It’s representative of where most Apple software and hardware is designed and where their customers have atypically high disposable income compared to most other countries. They’re obviously doing pretty well with this strategy.
We were using whatsapp before iPhone even came to my home country, and living in Ireland now, everyone seems to be using it here as well. In fact, I'll venture as far as saying /not/ having WhatsApp is considered weird and you will no doubt exclude yourself from a lot of spcial circles.