Why Linear Tracking never took off?

One rationale for linear arms was to maintain perfect tangency to the groove, following the track of the cutting head across the lacquer. In comparison, pivoted arms are truly tangent at only certain radii on the record, and this can result in distortion.

Linear tracking arms are far from simple in operation. TWL mentioned air bearing versions with pumps, and there have been others with multiple rotating rods or servo motors to facilitate the arms' lateral mobility, especially as required to track off-center records.

Tassiemike, Thanks for the perspective on the Zero 100. I remember looking at one back in the 70s, before I knew anything about hifi. I was intrigued by the nifty solution that the articulating cantilever design provided for linear tracking. I recall the salesman badmouthed it, disparaging the design by claiming the cantilever assembly added too much mass and the extra pivots added too much friction and had too much play to provide satisfactory stability. The clincher was the unrefined auto return mechanism you mentioned, which turned me off as soon as he operated it. I got a Benjamin Miracord Elac 50H instead (still have it!). I'm glad to learn the real story on the Zero 100 from you, after all these years.