Its probably just cheaper. Honestly i am not sure how many pepole there are that usb 3.0 speeds are even a consideration when buying a phone. I honestly dont know how it works on iphones but i know many androids dont have usb 3.0 also. In fact ive rarely even seen usb speeds mentioned anywhere . I know my phone has usb 3.0 but i have ridicolously overspeced asus rog phone( which has 2 USB c one 3.0 and one 2.0 port and that’s probably the only reason they even mentioned it )