1) New elements are higher amperage than the kiln was designed for.
2) Loose push-on connectors over-heat the switch by creating a tiny electrical arc.
3) The kiln’s heat shield missing. (This is a sheet metal channel that helps guide heat away from the switch box. The heat shield is under the porcelain insulators of most kilns.)
4) A 120-volt switch is installed on a 240-volt kiln. Both switches look the same; the voltage is printed on the switch body.
5) There is too much heat in the kiln room. Switches burn up more frequently on hot summer days. In this case, use a fan to circulate air through the kiln switch box. But do not blow air against the outside of the firing chamber.