I have watched cardio kickboxing at gyms where they hit the punching bag type that stands on the floor
If you hit far enough behind the target then it will fall down every time
The majority of people do not know how to punch correctly otherwise the target would fall down every time
So they can not punch hard enough and it is not a matter of strength or power but technique
The only way to use those bags is to put them against a wall if you punch hard