Because new technologies will soon make it impossible to prevent counterfeiting.
According to the Treasury, they estimate an upper limit of 200 million of counterfeit is out there.
Meanwhile we add close to a trillion in official counterfeit from the fed every year. But that 200 million, roughly 1/5000th of counterfeit paper bills. THAT is the threat.
The vast majority of that according to some sources is in SE Asia. I also remember watching a documentary on the Colombian Cartel. Federal agents found an underground bunker in the jungle and first thought it was a processing plant, instead it turned out to be a counterfeiting operation. They were paying their low level people with fake US currency.