Calculating different rated power from the rated parameters for a delta AC motor
The rated power of a motor is the mechanical output power. That is, speed × torque.

The input power to a motor is the electrical input power. That is, line-line voltage × current × √3.

The motor is not 100% efficient. Some energy is lost in the conversion between electrical power and mechanical power.

Your 'missing' 3kW represents the motor's losses, including copper (resistive) loss, iron loss, friction, drag, spinning the integrated cooling fan (if any), etc.