” I tried the same technique with my own grandkids. Didn’t accomplish anything at all.”
I scolded a little kid knocking produce onto the floor in the grocery. He looked at me and said “you’re not my mom”.
That is a part of the problem. When many of us were children, and an adult told us to behave, even if not our parents, we usually did.
And if we gave lip back to them, we were going to get it from our own parents if they found out.
There are still plenty of respectful and well behaved kids out there. But there are also those who aren’t. What is different is the response of the parents in the cases of those who aren’t.