My impression is that teenage drinking and smoking was really huge in say, the 80s compared to today.

Frankly, often when I hear somebody like the commenter above I think they may have had some rowdy teenage years in the 80s or thereabouts and is kind of projecting that onto today's youth. "The laws don't work!" Maybe it wouldn't have worked for them. But in the time since...

Although, I don't think it's realistic to expect the laws to get consumption to zero. Maybe it's not even strictly the goal. Reduction, or mild taboo, is not the same as total elimination. People can still buy their kids sugary snacks. I give my kids sugary snacks in small amounts, but might support such a ban, because childhood and adult obesity is a pretty serious problem.