It’s because overhand bowling was just the way you bowled, so nobody considered making a rule to tell you that was necessary until someone didn’t. Imagine playing football and someone picks up the ball and- oh right ;-)
This gets the history a big wrong. Overarm bowling actually had to be explicitly legalized in the mid 19th century before it became common practice: https://www.theguardian.com/observer/osm/story/0,,782938,00....
This gets the history a big wrong. Overarm bowling actually had to be explicitly legalized in the mid 19th century before it became common practice: https://www.theguardian.com/observer/osm/story/0,,782938,00....