It could be marketing too. If all the Tincher kids use the glove block and pitch like clones of each other, then it becomes recognizable.
I second this. Since my last response we've seen denny again and the back swing is minimized. Helps her get get legs going and pushing out because she can get her arm rotation going and catching back up. In other words for my daughter too much swing causes her arm to get around too fast before the legs. This causes her upper body to be ahead and timing off. She will throw high to the left and twist upper body because it's so earlyI have two daughters pitching with a Tincher instructor. They’re not really big on marketing and I can tell you that nothing is done simply for differentiation. We’ve only been doing for a year but I can tell you that every move is based in science/physics and is another reason that their curriculum has evolved and is always evolving.
They’ve not ever emphasized a certain backswing with my girls, but like other high level coaches they understand the importance of the hips and core and how they are the engine of speed/velocity. Some amount of arm swing is natural and helpful to generating forward movement, Glove block allows pitching arm to travel loosely and freely.
I'm not certain why or how the backswing became so prevalent in the womens game.......the only explanation I can sign up for is that girls like rythm and the backswing certainly is rythmic. When teaching a young lady I try to find the pre-motion they are most comfortable with......until they prove it is not allowing them to be efficient. I have converted several pitchers over from a backswing to a traditional "mens out-of-glove (OOG)style" pre-motion. In every case the young lady threw equal or faster speed, improved her location accuracy dramatically, improved her spin axis, and eliminated the potential for the opposing team to pick her pitches. The conversion to the OOG style can be relatively easily accomplished.....sometimes in less than a week. I believe you will see an increasing number of pitchers using the OOG style.....especially with the increased pitch picking prevalent in college softball.
For someone to suggest that a backswing is an absolute is pretty difficult to comprehend. There is too much evidence to show any number of pre-motions can provide excellent results. The pre-motion should not be a "one size fits all" option.