Likely similar to as Juvenile-use alcohol use. Your snark is cute, but your reasoning flawed - people buy drugs (alcohol, tobacco, firearms, weed); If there's easier ways to get it that are taxed, those channels tend to get used.
Which to put a fine point on it is 100% taxed because adults buy alcohol for kids via the same avenues as for themselves. Nobody brews their own beer specifically to sell to teenagers.
