I think some are missing the point mentioned earlier that it is also about reaction time. Remember exit velocity is a product of bat speed. When you have low exit velocity you have slow bat speed. Now you have to commit to your swing just a tic or two earlier and are more susceptible to being fooled. And of course ball doesn't go as far or as fast. Also there are a lot of bad hs hitters. So it brings the average down. Good 12 and 13 year olds already have exit velocities - using bbcor - in the 70's.