I am normally on a 3-year phone cycle. In prior years, I remember around the 2.5 year mark I was practically itching for an upgrade. I remember in particular my iPhone 6 was laggy, slow, had too little RAM, etc. So when I got an 8 it was a breath of fresh air, and 3 years later I really wanted the bigger screen, camera system, and Face ID. Of course, there was the fresh battery as well.
It's different now. I have an iPhone 12 Pro. It still seems to work perfectly well. It is still fast (these CPUs seem to have hit overkill range somewhere around the iPhone 7) and responsive and (surprisingly) the battery has held up. The camera still takes great photos. So just for the sake of it I don't really see why I should upgrade. I hope Apple has more in store than this list. The iPhone 14 was (IMO) the most underwhelming upgrade - I don't like the dynamic island and outside of that they really seem to be running out of ways to convince us that these new upgrades are important and necessary.