It did have a lot going for it...Such as? OK, P-mount cartridges are quick and easy to mount. But the size, shape and weight of the standardized cartridge was very limiting for cartridge designers. Pretty much all of these were high compliance (soft suspension) cartridges that were very popular in the 80s. Also, most of the tonearms for P-mount were cheap and light, with little or no adjustment possible.
Not my cup of tea but maybe it's yours.