I just went from a launch day series 3 to series 7 when I learned they were dropping updates for the 3. I don't think upgrading every 3-4 years to the latest model is as out of the ordinary as you think. For me it's about longevity (some call that "future proofing"); how many years am I going to be able to use the product before I lose support?I can't even conceive why anybody okay such old tech as a series 3,4 or people with iPhone 5,6,etc would care about the "latest" models....they're not likely going to make that jump.
Mother in law just retired her 6S for a 13 pro as well around Christmas. She will probably keep that for five years too, assuming Apple supports it as long as they did the 6S.🤷♂️