Everyone who has an iPhone uses iMessage as a main communication app. Nobody bothers to replace their default SMS client and literally all banks, institutions, 2FA and key communications rely on sms to work.
The fact that most people seem to prefer to have their personal or business chats on WhatsApp is secondary to SMS and iMessage (on iPhone obviously).
9to5Google: iMessage for Android doesn't matter, just use good apps (9to5google.com)