Why do people call police fascists?

There are many reasons. Many just hear the word in ping somewhere and just apply it generally, it admittedly sounds cool. Others may know the meaning but have no context to put with it and apply it improperly. They may have never left the great U.S. and actually been to a communist or dictatorship country having no idea how good things really are here. So it is probably a mix of ignorance and misplaced anger.