Because Beacon is a prestigious school for Hunters and Huntresses, who are expected to protect the world and it's peace? I'd imagine that they would not allow their students (Most who should be around 17 years old, mind you) to be using illegal substances or partaking in activities reserved for adults, regardless of their aptitudes. Sure, Physics might have gotten shanked in the ribs ever since the trailers revealed themselves, but Beacon is still a school with certain standards. A fighting school mind you, but not some cheap inner-city school were delinquency is accepted. Usually.