"I mean, the death in the late eighties and early nineties really shook out a lot of hacks. The pond just sort of dried up for a lot of really bad comedians"

This quote by Patton Oswalt is referring to the funny scene in the late eighties and early nineties. He is saying that the death of lots of famous comedians during this time duration had a considerable effect on the funny market. It triggered a lot of "hacks" or unskilled comics to be removed from the scene, leaving just the more skilled comedians. This led to a "drying up" of the funny pond, implying that there were fewer bad comics and more talented comics. This quote is a testament to the effect that the death of these popular comedians had on the comedy market, and how it altered the landscape of comedy for the much better.