Other than a few people who absolutely must have the latest phone, I only see two reason why people replace their phone: 1) Battery is no good. 2) Operating system has stopped getting updates and they can no longer run that one or two apps they really need.

Replaceable battery and 10 years of OS updates and a large percentage of people would stop upgrading their phones. There hasn't been much innovation in phones in the past 10 years. If the battery hadn't died and the OS was still updated there would be zero reason for me to not be using my iPhone 7.