The rule obviously exists for two primary reasons:
- To minimize unnecessary wear and tear on equipment.
- To reduce the risk of injury.
Whether you view these as significant concerns is subjective.
High schools often lack replacement rims and backboards, and many may not have the budget to replace damaged equipment in a timely manner. During pregame warmups, players dunking uncontested are often doing so for show, attempting to dunk with more force than they would in a game situation, where dunks are typically contested or occur on fast breaks.
That said, as others have pointed out, modern equipment design has improved. Many rims are now mounted to the frame or stanchion rather than the glass backboard, significantly reducing the risk of damage — even from the most aggressive dunks.
Is the rule based on outdated technology and standards? Yes.
Can we confidently say that all schools have upgraded equipment, making the rule unnecessary? Not yet.