Pot is NOT legal in the US -- at least not from Federal Standards -- the law is just not enforced. It is "legal" in many States as far as State law. Employers who test will state that it is illegal in Federal Law. Insurance companies must continue to feel that there is a lowering of standards (safety, judgement, etc) by those who use pot because it is the insurers who push business to drug test in the name of "safety".
Example, If the driver at my trucking company caused an accident and tested "positive" for drugs (even thogh it was 2-3 days since using drugs), that information would be used in court against the business (liability is to the insurer). It's all about the money. Legalization is all about the money. The motive of State legalization is so they can tax it. Like almost everything -- Follow the Money!