Corporate cost reduction is why companies drug test.

They receive huge breaks in the cost of health insurance they provide and accident insurance that they pay the insurance companies.

There are all kinds of things that companies can do to recieve "breaks" in the cost of insurance that they pay:

Nicotine testing is now becoming more and more prominent as you will see significant cost passed onto you by the employer if you smoke cigs. Some companies wont even hire you now if you smoke cigarettes.

Obesity is now being looked at as well. It's fucking crazy man.

If your employer provides a work out room where you work, the compoany is recieving a break in their insurance costs.

Many more things, but needless to say drug testing pre employment and randoms after hire are huge cost reductions, and will never go away!!