Not a scientific answer, but because they are immature.
Different medication, re-examination, or lower dosage
There are different factors that may encourage substance abuse. Those factors can include stress of studies, trying to fit in because usually everyone at college parties do such kind of things, trying to get over something such as heartbreaks and even some substances help to become more hyper active and help with college errands.
However, there are also some reasons that might help a college student to stay away from such things. Those factors can include health reasons, parents pressure, college rules and even self-restrain
