Rod1957, in direct drive turntables of the vintage sort, the platter is actually part of the motor, and the spindle bearing is actually also the motor bearing.
Since motors vibrate, and since the motor bearing is not nearly built to as close-tolerance as a normal TT main bearing, there is unwanted movement in the platter of most of these vintage DD designs.
Additionally, there are spinning magnets(under the platter - part of the motor) which are very close to the cartridge at the inner part of the record. Since the platters are also metal, there is not much stopping magnetic effects of these spinning magnets on the cartridge magnetic fields.
Third, most of the vintage DD designs use a quartz-lock speed controller with a very lightweight platter, which results in "speed hunting", in a fairly audible "flutter" frequency, and gives unnatural sound overall, compared to other turntables.
Fourth, most vintage DD TT's were mass-market designs and cheaply produced out of plastic, and were never really anything out-of-the-ordinary, even when they were new. Most of the arms were quite poor(or at best - adequate), and sufficed primarily for the low cost MM cartridges that were expected to be placed on them.
Let's face it, these TT's were the "Volkswagen Beetle" of the time, and never were even intended to be thought of as anything very good. They were mass-market plastic equivalents of today's "Coby" CD player for $24.95
The better ones, like Micro Seiki and the higher level Denon, and the Technics SP10(and yes, even the SL1200) were a bit more expensive, aimed at a higher performance market, and did sound better than the cheap ones. However, ultimately they faded away as the belt-drive revolution took over and killed most of them off.
You can say what you want about belt-drives, but they did kill off most DD tables permanently. This was not an accident.
