Think of a strobe. Perhaps it's only catching it synchronously.
Say it's going twice as fast, you're only seeing it once for every two rotations.
Of note, a pure synchronous electric motor must set spinning at a proper rotation speed to sync with the applied electrical input, thereby maintain rotation. It is not self-starting.
The optically driven rotor likely is not synchronous with the light applied. The circularly polarized light does manage to provide an offset momentum kick to the rotor ends, which results in rotation from startup.
I feel like an ape looking at threads like this and the replies that follow because this is so far above my head..... Thanks to my fellow Freepers for shattering the notion that Trump supporters are science-denying dummies!