The "proper" bowling technique is there to partly help to gain accuracy, but as far as I know they're to prevent injuries as well. I know I shouldn't lift my legs up during the release, now that I have seen these pictures, I'm pretty darn sure I lifted my left foot up on each of my releases 😂
Speaking of physically demanding sports, bowling indeed not one of them. But then, as a NOT regular bowler, every time when I put my hands on those balls, I will have a sore shoulders and forearms the next day 😂