It is a question of security . In the 1950s, the de Havilland company found that the in-flight accidents suffered by its Comet jets, equipped with large windows, were due to the fuselage breaking at the corners of the windows due to metal fatigue . Thus, these were redesigned and made smaller and rounder. The window of an airplane is made up of two pressure panels and a third interior panel that prevents passengers from accessing the others and having an accident.
A windowless plane would be cheaper to build, safer, and have more cargo capacity.
