A couple of points...
First off, I'm fairly certain that for at least the past few years, KOOL has been playing the 80's version of Casey's show.
Second, from a programming perspective, I can kinda understand the decision. You want control over every single song that goes on your station all the time, and for those few hours that Casey's show is running, what your station is playing is totally out of your hands. Plus, since Casey's show was just a repeat of his (in this case) 80's broadcasts, there were bound to be some stinkers down at the lower end of the countdown. Sure, some listeners might be pleasantly surprised to hear "Take It Easy" by Andy Taylor of Duran Duran or "Respect Yourself" by Bruce Willis (seriously, that charted), but familiarity breeds contempt and ratings, unfortunately.
Finally, it's also an unfortunate fact that Casey is quite dead. I can see why Premiere would want to squeeze some dollars out of his legacy, but come on...NPR stopped producing reruns of "Car Talk" a couple years ago, and one of those guys is still alive! Don't get me wrong. I loved listening to Casey, and somewhere I still have a cassette of the infamous out-takes, but it's time to let the man rest.
p.s. Take It Easy by Andy Taylor was actually not half bad.