Every drug except cannabis is flushed from the system as fast as alcohol. If someone is being tested they simply wait or say they cannot urinate that moment.
There is no panel that includes the millions of possible designer drugs and all the new ones that are being made every month. If someone is randomly tested, they can simply use these more dangerous designer drugs instead of the safer known ones.
There is no test for people who abuse various legal Rx and OTC drugs. I.e. if you abuse cough syrup or sleep meds it will not come up on a test. There is no test for people who sleep poorly or work too many hours.
Working too hard and being sleepy if far more impairing than cannabis yet nobody is screaming to test or outlaw commuting for late shifts.
And your point is? Federal drug testing or any drug testing is not a 100% fool proof method, and it was never sold as such.