also capacity. larger plane need larger wing that enter into transonic regime earlier than smaller wing. http://www.aerospaceweb.org/question/aerodynamics/area

also capacity. larger plane need larger wing that enter into transonic regime earlier than smaller wing. http://www.aerospaceweb.org/question/aerodynamics/area-rule/transonic-drag.jpg http://www.aerospaceweb.org/question/aerodynamics/area-rule/... https://en.wikipedia.org/wiki/Drag-divergence_Mach_number https://en.wikipedia.org/wiki/Drag-divergence_Mach_number you want to be below or above transonic, and above transonic is banned pretty much anywhere.