Incorrect meme, almost no one is on whatsapp in Hungary for example. We use Messenger, Viber mainly and other social media apps that have a chat feature.
Common case of people seeing that something is common in Western Europe and Latin America and then claiming “the U.S. is the only country that doesn’t do X”. Happens all the time.
So basically you are making my own argument: we use tons of different apps. What would be the selection screen useful for?
Going further: if we download different messengers, it stands to reason we can download different browsers, therefore if safari is the most used it's because it's the one we choose.