I think what's probably happening is a subtle crossover between the instructor wishing to maintain a safe flight deck and an instructor trying to convert a prospect into a customer.
If the prospect can apply power and keep a straight line down the middle, apply a little back pressure when suggested, but not too much, the feeling of elation and confidence will convert to $$$ in the till and a happy new punter in the left hand seat, and a happy chappie in the right-hand seat who can afford to eat again.
Just saying, instructors are between a rock and a hard place. Both salesperson and quality controller. Hmmm...