That's because kids are being brought before judges and told "treatment or jail" for using pot more often than for using alcohol.
The previous dodge was:
Oh, I see. That's it, eh? (eye roll)
Every single person I've known in "treatment" programs for cannabis has been forced there by a judge or by threat of criminal sanctions. I've know personally and am aquainted with many that know someone that had to take "treatment". None of them volunteered.
If you think there are, provide us with some documentation. 