It could also not be used much because it's too crude. You'd either be affecting anyone in a area, or you'd have to have equipment to aim it, too much work.
When a boss can look at their company dashboard and see where productivity is dropping and touch their phone to accurately send precise pain that causes no physical damage exactly to those underperforming, we may see usage increase.
You may not see it at McDonald's in California right away, but I'd be shocked (pun intended) if not a single sadistic psychopath in the world never tries it. And if they are not stopped, they will win capitalism being more productive.