I feel there will always be people with small hands, or a physical hand or arm disability which make owning a smaller smartphone easier to use.
There are also people who secretly use a smaller smartphone in school, jail, and work because they feel they are less likely to get caught using a phone if the phone is smaller in size, so some people who want to secretly use a smaller phone will buy one.
Using a smaller phone may also feel more private because people can not as easily see what you are viewing on your small phone screen when the user is a few feet away from you.
There are also people who secretly use a smaller smartphone in school, jail, and work because they feel they are less likely to get caught using a phone if the phone is smaller in size, so some people who want to secretly use a smaller phone will buy one.
Using a smaller phone may also feel more private because people can not as easily see what you are viewing on your small phone screen when the user is a few feet away from you.