Michael Fremer put it well when he wrote:
"Regulating a direct-drive motor's speed with a phase-locked loop produces tight speed control and measurably low levels of wow and flutter, but the motor's constant, ultra-high-speed hunting and pecking as it over- and undercompensates in the attempt to produce a consistent speed can create a jitter effect in the mid-treble to which the human ear is particularly sensitive, adding a hard, brittle texture to music. That describes the sound of Technics' now-discontinued SL1200 series of direct-drive turntables, and explains why, despite their high build quality and relatively low price, few are used in serious audio systems, though some listeners claim that these 'tables can be modified to improve their sonic performance."
Certain direct drive TTs have overcome that problem principally with very heavy platters imparting a strong fly-wheel effect. They are very expensive though going back to the Goldmund, and more recently the VPI and others
As with most things, hearing the problems may depend on associated components and the discrimination of the listener.