alt Hacker NewsAmericans primarily use iMessage/SMS/RCS. You only need one messaging app and everyone has it pre-installed on both iOS and Android.
WhatsApp does not solve any problems for the typical American user. Most Americans don't install WhatsApp unless they spend a lot of time overseas some place where it is required to do anything. Even international group chats seem to be more Discord-based in recent years.
What I like about WhatsApp is that I don't need a Google account to use it on the computer. I don't use Google messages or even a Google account on my android phone. So I have no RCS and I don't even look at SMS.