Decline in teen drug use continues, surprising experts

It’s probably because previous generations are becoming okay with drugs and millennials tend to be in favor of more permissive drug use.

If parents think it’s cool, teens won’t.

Pretty clear cut to me.

Yup this is exactly it. In the middle class UK even cocaine use is normalized. When your parents are smoking weed, doing lines of coke, and drinking excessive amounts of wine/beer, it's not exactly cool.