I have no idea why. It is a 3 phase AC synchronous motor. Synchronous motors are best for turntables because they will automatically adjust torque to maintain the speed dictated by the AC signal they are given. It happens instantaneously. I suspect they are just miss-informed.
The SOTA motors are a BLDC type, also known as EC motors (electrically commutated). These motors can be driven a number of ways. They have 3 windings and hall sensors which can be used to signal the control circuitry when to commutate or switch the currents in the windings. Only two of the 3 windings are driven at a time and the control circuitry can also change the polarity of the drive signal the same way a mechanical commutating ring changes current in a DC motor. When driven this way, they behave very similar to DC motors where the DC current dictates the speed. Without an external feedback loop, they will also exhibit poor speed stability, slowing down under load just as DC motors do. Besides poor speed stability, the motor can also exhibit increased vibration when driven this way.
If driven by 3 sinewaves, the motor behaves very similar to an AC synch motor where the frequency determines the motor speed rather than the drive level. The drive level needs to be adjusted by the control circuitry as the speed changes to compensate for the change in back EMF in order to maintain torque and reduce vibration. This is much more sophisticated than the simple block commutation controllers and is how the SOTA motors are driven. It is rare to see this level of sophistication on tables under $20K.