It’s a common elemental theme we see across stories, fantasies, etc. It seems like it is an element that should be part of that pantheon but maybe there is a scientific explanation of why it isn’t? Or is it simply, they did not have enough understanding of it at the time those 4 were suggested.
not sure what stories and fantasies you like reading, but most elemental magic systems i know of usually contain electricity as one of the elements. mostly a manga reader here.