A little off the original topic but I have a few opinions to share. The original rule, as I understand, dealt with the infamous "crow hop" as it was named. As time went on it became apparent more description was needed as people argued over the exact movement to constitute a crow hop. That's when they must have decided to add the "leap and replant" along with other wording to describe an illegal pitch due to the footwork of a pitch. There are still many other factors such as the ball to glove part of the rule that can constitute an illegal pitch.
This is what helps me deal with and understand the reasons why pitchers do what they do. In most cases, it is my opinion they are not doing it purposely to gain an advantage. It simply means they "forgot" what they had been taught. An umpire calls an illegal pitch and without complaining she throws it correctly the next pitch. That's because the umpire's call reminded them---------not because they got caught and corrected. There are so many things that go into purposely throwing a legal pitch that the kids simply forget a step or 2. We work on those very things at every lesson here. They are trying to learn a new pitch and simply forget. No different from trying to deliver that pitch in a game and they forget.
The crow hop and leap and replant scenarios deal with a host of issues. The worst being an instructor not doing their job. You don't continue to take the familiy's money and teach a kid how to pitch with illegal footwork. It's simply unethical. For most kids they go thru periods of adjustment, especially when trying to step up their pitching game to a higher level. There arm spin gets out of synchronization with the lower body. This promotes the other things to happen. If instructors would correct this instead of ignoring this timing issue, the kids would be aware and alert to fix it. Teaching methods really come into play but it takes a trained instructor to see the signs and correct a bad habit from becoming a chronic problem. There's more to this pitching thing than spinning your arm and stepping forward.
Again, I still don't believe most do the things on purpose. It's a matter of exceptions to the rule or girls simply being taught wrong and unaware.