That is not as clear cut as "common knowledge" would indicate. See e.g.,
Prevention of spinal cord injuries that occur in swimming pools which found that 76.8% of spinal cord injuries had no diving device compared to 8.6% with a low diving board. Over 95% of injuries were in depth <= 8 ft, with 57.2% due to diving into <= 4 ft. There are other sources with similar statistics. Diving boards are, by design, located over deeper and safer water. If kids are going to jump into the pool anyway, isn't it better to encourage that jump to be over deep water?