Why is the electric field inside a conductor zero during electrostatic equilibrium?

In a state of electrostatic equilibrium, the electric field inside a conductor is zero because any internal field would exert a force on the free charges within the material.12

If an electric field were present, these free charges would move in response to the force until they reached a new configuration where their collective contributions to the internal field perfectly cancel each other out. Once this redistribution is complete, the charges settle into a static arrangement, typically residing on the surface of the conductor, and the net electric field inside the material vanishes. Because the internal electric field is zero, no further movement of charge occurs, and the entire conductor remains at a single, constant electric potential, making it an equipotential volume.123