Why we did't use 100% copper in electric fans?

A lot of copper alloys are used for different purposes. If the motor has a commutator, that is tellurium copper. If you look at a plug and see a copper colored screw, that is tellurium copper. If there is a copper colored spring, that is phosphor bronze. Wires are usually 95% copper and another metal to keep it from crystallizing when it flexes. And many more possibilities.