Dave, I think the answer is simply that a player is required to make a "shot" rather than some other sort of movement or act with the cue stick. A "shot" (paragraph 8.2 Shot) requires "a forward stroke motion of the cue stick."
When you are in tight quarters and want to move the cue ball only slightly -- and your nerves are jumping from pressure (or old age, ha!) -- a legal "shot" is sometimes difficult to perform. It's certainly more difficult than some of the other movements you mentioned.
Certainly you are correct in your statement, but the issue is why is it an unsportsmanlike conduct issue and not a simple foul.