There is so much time, effort, and physical waste that is generated by slightly redesigning phones every year purely for the sake of making sales (as opposed to meaningful improvement upon the existing design or introduction of a new hardware feature). Think not only of people upgrading for the sake of it, but all of the cases, screen protectors, and other assorted accessories cast in plastic for previous models that are garbage now.
It would be nice if we could just space these things out to 5 years or so now, because that's probably how long it takes for anything to change enough to justify a new model.
It's not like the incremental physical changes just automatically happen independently of designing, mass manufacturing, and releasing new phone models. The incremental physical changes happen because companies are trying to develop new phone models.