If you would happen to find a switch that has no exposed metal parts you would not have to ground it. I sure hope this would be obvious to installers and inspectors, but you never know. There are surface mounted devices with no metallic parts other than the conductive parts that make up the switching components themselves (try grounding those and see what happens:happyyes

that would not require a grounding conductor, but they often have grounding terminals mostly for the convenience of landing / splicing grounding conductors that do exist.