If you look where the market has shifted, The iPhone SE as popular as it is, still primarily is a very small demographic consumers who would be willing to upgrade to that specific model iPhone, because it is dated in terms of specifications and hardware. I think iPhone SE serves three purposes, (1) first time iPhone buyers and (2) for those who specifically who are not interested in having the latest technology, but ultimately wants the smaller form factor. (3) Being a global phone in other countries like Asia and India where the other iPhone models are unobtainable because of how expensive they are.
The overwhelming trend of those who have upgraded to larger phones has been on the rise for years because of two things, the larger display and longer battery life. Also with larger phones comes included having more technology and camera capabilities. That’s where the marketing really is if you look at the trend of how smart phone manufacturers are trying to shift the consumer to purchase the most expensive, largest smart phone available.
For example, when the iPhone 7 released, almost 90% of Apples marketing was geared towards the dual camera introduction with iPhone 7 Plus, hardly any marketing was even given to the 4.7 iPhone model.