Why would the catalytic converter have to be replaced 8 times in a 1997 Chevy Monte Carlo first at 37000 miles purchased new Service department replaced all possibilities and say they do not know why?

Generally, unburned fuel getting into the converter is what damages them. How is it running?, what size engine? What did the dealer say is "wrong" with the converters they are replacing? -->You can easily damage your catalytic converter by making a lot of very short trips and not allowing you car to properly reach operating temperature.