Not too many PRR MP's survived. Nor too many LIRR's and NYC's and NH's either. RDG had quite a few picked up by tourists lines. But the best answer proffered so far is that there were so many DL&W cars at the same time and at the right time and at the right price. While you can count the number of LIRR, NYC, and NH cars on your two hands, you need your feet to count the RDG's. You need much more to count the DL&W cars although you can probably count the number of places you'll find them on your hands. And feet.
That's true Henry,
Timing was everything, and the right price just made everything line up.
It's a shame we lost so many PRR, LIRR, NH, and other EMU's but the Edison cars look great behind steam or early diesels at museum. Sad but true another 2 LIRR MP class cars have been cut up.
When the cars were retired and sold off for other use was friction bearings still permitted for interchange?