Because of arrogance, frankly. I have been called 'anti-American' for pointing out something similar. There are many people who are blinded by nationalism and patriotism and cannot fathom using other countries as models of what may work in a more effective fashion. The irony is that many of those countries have been the targets of terrorism for decades longer than the US, and on a greater scale. They have had the time to figure things out, and could be a good model for TSA. I've been through at least 6 non-US airports in the last 2 weeks and my shoes have not alarmed; I tossed those Aerosoles and replaced them with GEOX, my usual travel brand.