Explain why the current is reduced as electrons move through a conductor.

The current is reduced as less energy is available to move electrons through the wire.

This is because electrons moving through the conducting substance collide with the electrons and ions.

This causes collisions which further more convert kinetic energy into thermal energy because of the fewer energy that is available, it reduces.

Moreover the resistivity factor of the conductor it self might play some role and the loss of energy too.

As current moves through the conductor; the resistance of the conductor causes the original amount of current to reduce do to the length and the cross section size of the wire.