I'm guessing they've seen kids get "too" tall whereby they lose their athleticism. There was a discussion on here a few weeks back about pitcher's height. There seemed to be a sweet spot - based on MLB pitcher population - of I believe 6-2. All that said, there were really good pitchers under 6-0 and really good pitchers over 6-6. As long as the growth does not present problems with mechanics - and all things are still moving together at the right speeds - then the additional height becomes an advantage. I personally think they are simply playing the averages - but averages go out the door when you are talking about the individual.