This might be hard to understand unless you realize that metals aren't made of separate atoms. A metal object is like a jar of water. A metal object is like one giant atom with many nucleii but only one electron cloud. And in an electric circuit, the power supply is not the source of the electrons. The power supply is simply an electron pump.
Metals are different than other materials in that they store heat energy as wiggling electrons.
If you try to force the metal's electrons to flow along, those electrons will speed up at first. But then they will be deflected by other electrons which had been trying to orbit around the non-moving atoms. They fly in all directions with no average drift and no overall electric current. Speeding them up doesn't push them in the direction of the current. Speeding them up makes the crowd wiggle faster.