That is a common mistake about penalty strategy but you must stop thinking that a goalkeeper who didn't move is idiot or not-trained ...
The choice not to move is no less rational than the choice to move, actually it is maybe more judicious.
People, and directly the keeper, tend to prefer seeing the goalie dive, even on the wrong side, than staying on his feet, though the result is the same no matter how close he was to the ball
There is more to say about penalty psychology, thus I invite you to consult this interesting article https://www.sciencedirect.com/science/article/abs/pii/S0167487006001048