I used to work in the touchscreen space, and from what I've anecdotally heard is that screen makers take little or no input from their customers, unless you are

I used to work in the touchscreen space, and from what I've anecdotally heard is that screen makers take little or no input from their customers, unless you are Apple or Samsung. They are doing fine with the big sizes, maybe they have determined that releasing smaller phones will cannibalize their sales or they don't want to adjust their software for two screen sizes. And smaller vendors can't get customized screens for a competitive price, so they have to take what is on the market. You see the same phenomenon in the laptop market. Device size is designed around screen size, and you can only get certain sizes like 13.3", 15.6". Apple is one of the few companies that controls their own screen manufacturing.