In an effort to be more clear, I believe that the waistband and collar checks are primarily used to get the gloves in areas where they suspect that people may have hidden explosives. It is not to find the explosives, it is to get the traces on the gloves for testing. When thwarted by the particular clothing that someone is wearing, it creates a difficulty getting the "sample" for the ETD test. They also rub down the top of my socks which would give an indication if I had something in my shoes.

Restated, the primary purpose of the rubdown may not be to find the hidden explosive but to find the evidence of the hidden explosive. Some of the strange techniques and their insistence on their being done point in this direction.