Because there is no current flowing in the rotor, and thus there is no magnetic field in the rotor, and thus there is no torque between the rotor and the field.

What is a rotor?

the blade is called rotor blades
The rotor blades on top are called Main Rotor Blades, because they are the main source of lift for the helicopter. The smaller rotor blades on the tail are called Tail Rotor Blades.

The rotor head changes the angle of incidence of the rotor blades as they rotate.

Wound rotor and squirrel-cage rotor