Where did they go ? Perhaps if retailers had been less keen to install The Mosquito (https://en.wikipedia.org/wiki/The_Mosquito) to shoo them away, they may have had more customers.
Sounds like retailers have discovered the downside to the constant anti-teenager policies of malls and shops treating them as hostile aliens to be driven off and sometimes even criminalized for being so "anti-social" as to try and go out shopping by themselves whilst under 21.
No wonder they buy online or just decide to play online games instead of going out. At least there they are not going to be harassed by mall cops or arrested by real cops and criminalized.