Again, this is my opinion and I can't prove it. But my intuition tells me that among younger members, say those with less than 10 years of service, 4 or 5 years in, for example, a certain culture has developed in some units. It is seen as cool. Certainly, like anywhere else, people don't shout it from the rooftops, but it is known within their group, and they party hard on the weekend.
As I said, members of the military try to get around the screening policies. Cannabis is cheaper but riskier when it comes to testing. Cocaine is more expensive but less risky in terms of testing. The drug problems today are a bit more complex than they were when people stuck to cannabis.