The reason wasn't politics. It was something called PPM, as in Portable People Meter. This is a new method Arbitron uses for measuring listenership to stations. With the debut of PPM in the market a few years ago, KGO's ratings went down, while the ratings for all-news KCBS and public broadcaster KQED (now the #1 station in the Bay Area) went up. Essentially, KGO and its new owners are trying to compete with those two stations.
Blowing up KGO as extremely as Cumulus did wasn't a very bright idea. For one, there's no way they can compete with what KCBS does. Second, Cumulus likes to run things on the cheap, and that won't work with an expensive format like all-news.
All-news seems to be the latest du jour format. Doesn't skew as old as talk, gets high ratings and brings in lots of money from respectable advertisers (as opposed to partisan political talk). Just this year, upstart Merlin Media launched FM news stations in New York and Chicago (and got promptly and rightfully laughed at), Radio One, of all companies, launched one in Houston which has gotten decent reviews, and CBS launched a WBBM simulcast in Chicago, with a new station to launch in Washington, DC next month. And Merlin might launch another all-news station in Philly sometime next year.