Because people are stupid and children make poor decisions.https://www.yahoo.com/news/three-charged-murder-colorado-rock-064213316.html
I wonder sometimes why this keeps being a thing. I remember a couple decades ago there was a thing going on around here with some youngins that were dropping big rocks off of the interstate overpasses. People got killed and others seriously maimed. I have been hearing about some of that on the news again lately.