Why are many Americans so resistant to adopting the metric system though widely used in military and industry?

Its to expensive to switch. Americans are actually open to the metric system and it has been brought up many times in congress. The only thing stopping it is that it would cost way to much money to change everything that is already written or calibrated to the English system. We teach both systems in school anyways and once in college everything is metric so I wouldnt say we are resistant.