The coupling between the platter surface and the base of the tone arm must be as rigid and dead as possible. To this end, the bearing can have no slop (but at the same time can't make noise and has to be free) and the plinth be as rigid and dead as possible. Anything short of this will be interpreted by the pickup as coloration should any vibration be introduced. IOW the base of the arm has to vibrate in the same plane and rate as the platter so as to be unable to interpret the vibration as a signal.
Obviously a magnetic suspension flies right in the face of this.
Obviously a magnetic suspension flies right in the face of this.