In basic electric motor terms, they are constant torque sources, so the spindle only produces 2.2KW at the rated speed.
Half the speed, you half the power.

You can use methods to boost the torque at lower speeds, but you risk overheating the windings, and there is a point at which cogging becomes an issue, as AC motors rely on inertia to a certain extent to smooth out the acceleration/deceleration between phases.