There is also supply and demand at work. In the days of yore, when Cleveland was a top market and there were maybe 10 major radio stations, with possible ratings of 15, 20, even 30 shares, only 3 TV stations and a couple of newspapers, the supply of commercial availabilities was much smaller, hence radio could charge a high price for spots, often playing fewer spots at higher cost because they could. Now, with dozens of radio stations, hundreds of TV channels, and an almost infinite choice over the internet plus a market that's half what it was, the supply of advertising choices is far greater while the advertising dollars percentage wise are still much the same. That means proportionally lower spot rates and more spots needed to pay the light bill and other costs which have also risen greatly.
It's still a free market and ultimately the free market will shape the industry.