Low Hours Phono Cartridges?

The answer is simple.

Many sellers are DEALERS.

Most sellers are ordinary guys/girls who are true and honest audiophiles like me. They often have multiple cartridges, sell their old and buy new. I have bought a dozen vintage and a couple of NOS carts from A´gon and eBay and all have been OK, and I have sold maybe ten used and one NOS to fund my next cart/audio purchase. Therefore actual playing hours are usually low because the cartridges are in circulation. It´s just fun to buy "low hours" carts for low prices. And actually most of my best used purchases are the best I may ever have: vintage MM, MF and MC. My maximum is 300 hours, if it fits my system and I like it I keep it.
I have had bookkeeping for all the LPs I have played and know exactly how many hours my cartridge really has... since my first real high quality cartridge more than thirty years ago.
Audio life is simple : ) Enjoy your darlings 

>>I am wondering why every phono cartridge advertised for sale has low hours?<<

For the same reason that every driver stopped for suspected DUI has consumed only 2 beers. 

"lawyer living in the US. He said 30 hours and I believed him"  

I have always been leery of " very low hour Cartridges" . The reasons, no way to verify it and secondly no way of knowing it was set up properly either. The real news here is someone actually believed a Lawyer, a Lawyer selling a "low hour cart" ,..... for many that's a postman always rings twice scenario for cautious skepticism  ........... 

I have a note pad next to me while listening.  Each lp side gets a check mark to track usage.  Each side is 20 minutes or so, pretty easy really to track.