According to NewsBusters, reports that Sean Hannity left Cumulus due to the company’s failure to properly manage its stations are borne out by the evidence. All of Cumulus’ top stations’ ratings have tanked radically since Cumulus’ takeover in September 2011:

Cumulus contends that the ratings decline is due to Hannity and Rush Limbaugh but in Los Angeles and New York, Hannity and Limbaugh outpace the rest of the station by leaps and bounds. KABC is down 62% overall, but Hannity is down just 13%. WABC is down 45%, but Hannity is down just 3.2%.