They do that with cigarettes but kids still get them (atleast in my country). Banning a device is useless, beceause the same vaporizer could be used to other stuff, and it'd be still sold online (from places like china), and customs don't really check every package for what's inside (especially since it usually says "electronic gadget" on the CN22 form). Banning liquids would be easier, but in some places (eg, here), the liquids are sold separately as a mix of glycerins and a food-grade arome, where neither of those can be banned. Nicottine can be (and is), but while it's addictive, most of the "bad stuff" is in other ingredients, that again, cannot be baned easily. ...and you can also order niccotine concentrate online...

so yeah, it's hard. Making it unnatractive is a lot easier procedure with drugs and "bad things", but a machine that makes huge clouds of tutti frutti falvoured smoke is.. wel... fun.