I think it's mostly to discourage people from standing up at any point during the ride. No one who is sitting like they're supposed to could possibly fall out on the drop.
First time i ever went when i was 10(1985ish) we were standing outside HM at night of course and i dropped the camera i was holding i was so scared lol. So my sister who is much older then me wen on by herself while i was scared sitting outside waiting for her lol