I don't know that its neccessary to suggest there was a conspiracy against the flat arm NAD -- it may be significant that the initial positive response to the flat arm, and its current devotees seem to be using high compliance cartridges, and it very well may be that its an arm best suited to such cartridges.
Has anyone used it low compliance moving coils, especially heavy ones? It wouldn't be surprising if maybe it doesn't do as well with them. Given that the direction of the market at the time was strongly away from high compliance and toward moving coils, it may be that there just weren't enough buyers for an audiophile table (by which I mean tweaky and odd, and maybe full of inner beauty, but less so visibly) that was biased towards high compliance cartridges.
A similar fate befell the SME Series III arm, as wonderful as it was for the task it was designed for...