> Lots of iPhones in the US because of high incomes, and high iPhone availability

The US is not the only country with a wealthy populace which tends to use mostly iPhones. The UK, Germany, Switzerland, the Baltics, Japan, South Korea, Singapore, and Taiwan are all roughly equally as wealthy (if not more so) per capita. However, in literally everywhere else but the US, people almost exclusively use third-party apps like WhatsApp, Telegram, WeChat, etc. iMessage is completely ignored, and the Messages app on iPhones is used solely for SMSes from carriers, 2FA OTPs, and random spam that is ignored.

Furthermore, several flagship Android phones rival iPhones in cost now.