Sorry that you lost your opportunity this time...Any company that requires drug testing does so for a couple of reasons...insurance and workman's comp claims. Believe this they do not want to pay the exorbitant costs of lab testing but in the end it costs less to do that then to pay workman's comp claims and higher insurance premiums. I do not believe that any company anywhere will consider hiring a new employee that has already failed a drug test.
That's the excuse they use now. The main reason drug testing was implemented in private companies is because federal funding was tied to "the war on drugs". If you wanted to get or work on a federal contact, yout needed to drug test employees. If you didn't implement a drug screen program, no federal funds. Because 80%+ of our economy revolves around government programs, drug testing became ubiquitous.
It's a biased policy, cannabis users are unfairly punished because it doesn't metabolize as fast as cocaine, pills, alcohol, etc, etc. I saw perc addicts passing out at work, but the guy that smoked a joint 2 weeks ago at a party got fired, F'ed up.