The main reason that copper magnet wire can be used to wind a generator is that copper is a very good conductor. It has good flexibility and a good heat dissipation effect. Compared with other metals, it is relatively cheap. You can use any conductive material. But for economic reasons and physical copper is the best choice. In the late 1970s, aluminum was also used as a wire, but when the aluminum was heated by the large current flowing through it, the aluminum would catch fire. And it has other problems.

The rotating magnet in the copper winding generates electricity better than other metals (excluding silver and gold).

Copper is preferred because copper is a good compromise between conductivity and cost. As you pointed out, silver and gold are better, but who is willing to pay for them? Compared with silver, it is also relatively resistant to corrosion. It also has good thermal properties. Unlike aluminum, it does not shrink too much when it gets cold and will form an instantaneous oxide layer, which can cause bad connections. Using CCA wire can complement the advantages and disadvantages of copper and aluminum.