More like it isn't a moneymaker anywhere. Highest ratings for Air America in the country are a 3.7 share on a station in Portland. Not to mention, that entire entity filed for bankruptcy protection just 2 years ago 'cause they can't get anything going. Looking at those numbers, and considering Alabama is a red state all the way, I'd bet left-wing radio in Alabama would more than likely be ratings suicide.
I don't know about it 'not being a moneymaker anywhere', but Portland station you mentioned, along with prog-talkers in San Francisco, Los Angeles, West Palm Beach, Miami, and Madison, Wisconsin (on FM) are all Clear Channel stations, some with local hosts. The ones that have survived and thrived have probably relied much more on local advertising than national buys--but they're still there. One common mistake is confusing Air America as the only provider of progressive talk radio, when it isn't. Jones Radio syndicates Bill Press, Stephanie Miller, and Ed Schultz, the last of which has the most nationwide listeners. Jones, who also syndicates Clark Howard and Neal Boortz, certainly hasn't gone bankrupt , though it has been purchased by Triton Media Group.
Alabama as a whole is red, but there are a lot more purple places than you'd think. I would love to see one AM broadcaster in both Birmingham and Montgomery put an honest effort in marketing a progressive talk format for a year or two, and see what the results would be. We'll never know absolutely for sure until someone tries, but it's likely no broadcaster will because of the aforementioned risk involved. Alabama based callers have chimed in on both the Ed Schultz and Thom Hartmann midday shows, with XM & Sirius listeners and listeners online--and its through those subscriptions where the format's long term success probably lies.