Your iPhone Doesn’t Support New Apps

Besides not being able to update your iPhone, it’s also possible that you won’t be able to update your favorite apps anymore. Keep in mind that most developers keep supporting older devices for a longer time than five years — but sometimes they’re also limited by a need to drop support for older iOS releases.
So, if your favorite developer decides to stop supporting your iPhone — or the maximum version of iOS you can run on it, then you really need to consider an upgrade.
Moreover, older iPhones don’t get to use newer apps. Sometimes, it’s because they require a newer software update, and other times, it’s because they need a hardware feature that your iPhone just doesn’t have. If that’s happening to you, a new device is the way to go.