Why are non-metals generally poor conductors of electricity, while metals are good conductors?

Metals have a 'sea' of delocalized electrons that are free to move throughout the metallic lattice. These free electrons are responsible for conducting electricity. Non-metals, on the other hand, typically hold their electrons tightly in covalent bonds or have a complete outer shell, meaning they do not have free electrons to carry an electric current, making them poor conductors. Graphite is an exception among non-metals due to its unique layered structure with delocalized electrons.