Why don't people know how to manage their children?

I was in a restaurant just an hour ago with my parents and grandmother, and a child has been throwing a temper tantrum the entire time while we were trying to enjoy a nice meal. The kid was swinging on every chair and even kicked my dad's chair. At this point my jaw dropped open and I told the dumbstruck parents to learn how to manage your child. If you can't do that, then don't have any more kids. If I did that when I was younger, my parents would have dragged me to the restaurant and made me apologize. Although, I was always a quiet kid so I never gotten in trouble with my parents anyway. That's something I would have done with the child as well. Forced them to apologize to my father then remove them from the building.