Why Do Metals Conduct Heat And Electricity So Well?

Because metals have a lot of electrons inside them and there is space there the electrons can move freely. When electricity is passed or heat in the metal the electron carry the electricity or heat and spread it all over the metal. So the mobility of the electrons are the main reason why metals conduct electricity and heat  so well.
Shkumbin Abazi

The electron sea theory-

The cations in a metallic solid remain in stationary crystalline positions while the valence electrons from each metal are free to wander throughout the entire solid. Electrons are able to freely move around the entire solid. This helps with conducting electricity as well as dispersing heat. 

Because they are not French