I agree with you. The problem is that we conflate SMS and iMessage usage in the Messages app. Most people do use Messages for SMS-like messages (meaning not for exclusive iMessage features). E.g. looking at my message list: at least 40% of messages I receive are alerts, payment confirmations, appointment reminders, etc. These are SMS messages in terms of their purpose, even if some have the blue bubble and whatnot. Messages is a popular app in the US, but what we need to look at is how popular it is for specifically iMessage-exclusive features, not as an SMS client.