I doubt the data source can tell us this information. It asks students what drugs they have taken at what intervals, and does not seek to address the "why." Hence the pearl clutching by the NYT to provide the "why" for us.

Either way, we have no clue as to the harm that vaping causes us; we are rather certain of the harm alcohol, cigarettes and hard drugs cause us. The numbers in TFA are still pretty bad: ~17% of these kids have vaped THC in the past month where as ~50% had drank alcohol. Even if this was a tradeoff, it seems like a good one at this point.