Is Marijuana Use at Epidemic Levels in College Football?

In an article for CNN/SI, more than one NFL executive said that one third of the players that have first round grades for this year's NFL draft have admitted marijuana use. Some of the players from states with medical marijuana laws didn't even know that the NFL frowned on marijuana use. There are many people who argue that marijuana should be legalized because it is not "addictive". I would argue, why do so many people who generally are law abiding habitually use a substance that is illegal if it is not addictive?