How drug debt works? Either they owe money from the outside or they do pay someone to bring the drugs in and we do catch it. So they're out that money. Somebody owes somebody money for drugs they never received.
The same thing happens when they pass it around the dorms. People owe for drugs. If it gets brought in and distributed, somebody has to pay for it somehow. If they don't pay, they get their payment in another way, or they get motivated to pay.