Real answer: Apple hides scrollbars. Not just on iOS- on Mac OS they hide by default, and are only visible when actively scrolling. The vast majority of users don't notice them not being there, so nobody complains and designers keep hiding them.

Another fun thing: On Mac OS you can enable scrollbars to always show; but doing this adds a ~18px scroll gutter on every scrollable element, and thus breaks some scrolling web elements where the designers clearly only designed around the default. :)