As somebody who worked in advertising sales for a few decades, maybe I can shed a little light on the situation:
*I don't care what the so-called financial experts say...we are in the 4th year of the worst recession this country has seen since the late 1920's.
*Even with more than 90% of the population employed, a good chunk of them are earning far less than they earned 10 years ago, many are deep in personal debt, prices on necessities like gas, food, and so forth continue to get higher and higher...thus, many folks just aren't spending as much on non-necessities today...they just don't have it to spend.
*With the explosive growth of the internet...the public has a lot, lot more entertainment options than "just" radio...and major advertisers are spreading their ad dollars around...with an increasing share going to "new media" (digitial, websites)...and those digital ad dollars are coming from radio and TV budgets. Fewer ad dollars to traditional media.
What does all this have to do with so many format changes?
Radio groups and station owners are living in survival mode in a precarious advertising revenue environment. Radio is indeed a business...and rapid format changes reflect lost revenues. Sportstalk and to a lesser extent news and news-talk on FM is the new radio "silver bullet". Niche formats like smooth jazz, even some formerly mass-appeal formats become lost in the "we gotta make some money" shuffle. It's an economic reality....sadly.