Roger pointed out ."
There's a lot in that sentence. For pitchers with little or no strength in their core muscles - especially in the youth game, and definitely those pitchers coming off an injury (any injury), one style is usually dominate.
In the amateur game, what should come to the surface is asking a youngster "WHY" do you use that style all the time? Taking away the obvious - the set motion with runners on (generally), a coach should be far more sensitive to a "cause" more than an a "reason".
Another thing that I constantly see in orbit is this infatuation with velocity, in the youth game, and that includes high school varsity. In this regard, I think Zita has hit the nail on the head, sort of speak. A youngster that can control himself/herself with tossing strikes, from whatever comfort zone works, - "works".
I know there are issues with my posting here - not being of the amateur game, and that being said, more from the outside looking in. But, if a coach was to reason out why a youngster does what he does, as a benchmark of "reason" then perhaps, just perhaps, reasoning will give way to a "leave well enough alone", or, like Roger pointed out, a cause-n-effect approach to real coaching instead of "just do it this way."