In part because the Bush/Cheney/Obama regimes have made every American a suspect. The only civil liberty that has any force in the U.S. today is the law against racial discrimination. This law requires that every American citizen be treated as if he were a Muslim terrorist. The Transportation Security Administration rigorously enforces the refusal to discriminate between terrorist and citizen at airports and is now taking its gestapo violations of privacy into every form of travel and congregation: trucking, bus and train travel, sports events, and, without doubt, shopping centers and automobile traffic.
This despite the fact that there have been no terrorist incidents that could be used to justify such an expansive intrusion into privacy and freedom of movement.
The TSA has not caught a single terrorist. However, it has abused and inconvenienced several hundred thousand innocent American citizens.
The abuse happens, because people with authority are dying to use the authority. The absence of terrorists means that the TSA turns innocent Americans into terrorists. There have been so many absurd cases. One woman traveling with her ill and dying mother, who required special food, had contacted the TSA prior to the flight, explained the situation, and was given permission to take the special food onboard. But when she went through "security," the food was taken away, and when she protested she was arrested and hauled off, leaving the elderly mother in a wheelchair deserted.
Others have been arrested because a member of the household used a suitcase or carry bag to take guns and ammunition to the gun club or on a hunting trip and forgot to remove all the ammo, or the explosives test detected gunpowder residuals. Boy Scouts forgot to remove pocket knives from backpacks that they took on camping trips. Lactating mothers forced to give up breast milk. And so on.