Why are coreless motors all small motors?

The rotor coil of the coreless motor looks like a water cup, so it is called a hollow cup motor.

Its advantages are: because there is no iron core, there is no iron loss caused by the iron core, and the efficiency is high; because there is no iron core, it is light in weight, has a small moment of inertia, and is easy to control.

Its disadvantage is that because there is no iron core, the rotor coil can only be made very thin, and the output shaft has limited load, so the power of the hollow cup motor is generally not large, and the maximum is a few hundred watts. See the picture of the rotor coil below: