toly, your images show us that there can be wrist actions involved in strokes other than the serve. We are not denying that. However, your images do not prove that the terminology, wrist snap, is an accurate description of the actions involved. The primary problem with the terminology is that it is often misleading.
Have you done any actual coaching? While some players have produced the desired result when a coach tells them to snap the wrist, many others perform wrist actions that are counterproductive, stressful or even dangerous to the wrist. If one uses this questionable terminology, great care should be taken to demonstrate the desired actions. Further care should be taken to make certain that exaggerated wrist flexions (well past neutral) occur that can harm the stroke or the wrist.
The real problem here is that a student of the game may perform correct actions when told to snap the wrist but then they turn around and tell others to snap the wrist without proper demonstration and correction.
If u have one foot stuck in yesterday & one foot stuck in tomorrow, u are peeing on today.