Despite it's claims to the contrary,too mechanically complex,even the "simple" one is composed of several pieces which seems to transmit power through sun and planet gears,not direct torque.

Each separate mechanical piece composing the rotor is responsible for it's own mass,despite being linked together which would seem to impose it's own individual stresses resulting in frictional losses,not to mention inadequately tested sealing techniques. Just think of a mini-bike's centrifugal clutch.

One reason the Wankel was reasonably successful was due to the rotor being one piece,although imperfectly sealed.