There is a strong stereotype out there that Progressive talk radio will only fall and burn and has no chance of being a success while Conservative talk radio is immensely successful and will always succeed.
The rise and fall of one company (Air America) can not predict an industry or format as successful or not. There were several missteps including lack of proper funding and failure to own stations (they rented stations at too high of a price).
Fox News took on losses and low ratings for nearly a decade before becoming one of the most profitable cable channels with the highest rating in cable news.