If Entercom is facing fines over the FCC investigation, then that was a factor in this decision. When someone holds a prominent position for 20+ years, they may get complacent and feel untouchable. All employment is ultimately "At Will" and can be terminated with or without cause. Look at what's happening in the industry.
Reid was around when one of his PDs was fired for taking payola from record labels. He certainly is savvy enough to know the rules of the Radio Game. It appears he brought this on himself...
Back around 1986 I actually saw a music director (not in Buffalo) open up an overnight envelope from a record label. Guess what was inside? I'll give you a hint: You couldn't spin it on a turntable or cart it up, but you could definitely inhale it! I'm not sure what tainted the integrity of music radio more in those days, THAT kind of thing or the slimy "paper-adds". Of course those two acts were sometimes a tandem!