What was wrong with the P-mount ?

So, as some of you may gather, I know very little about turntables. I mean, I know the general physics, the RIAA curve, cartridge loading, stuff any one can pick up from a book.

Sometimes I think of getting into vinyl, especially with a store right across the street, the new Techniques turntables as well as old and new Luxmans or Yamahas, and then I remember the cartridges and all the issues of setting them up correctly, cleaning the vinyl, carefully holding the LP and I return to my digital only lifestyle.

One thing I was thinking about in all of this was, what happened ot the whole P-mount industry? Perfectly reasonable idea to me. Fixed dimensions for the cartridge, adjust the tracking force, and bam, done.

What went wrong?