This is the wrong way to look at it, unfortunately. More Fortune 500 companies doesn't mean they pay more for advertising space because advertising pricing ultimately comes down to audience numbers.
Not only do the Twins have, at most, a mid-market size of audience, that audience shuns cable television in greater numbers than other markets (going from older data from memory, I cannot find recent numbers).
And that's where the money is, cable television. And the Twins are working at a disadvantage there even compared to most other comparable markets, much less larger markets like Houston, NYC, or San Francisco.