While I am no expert on Sports Talk, people I speak with say Sports Talk sells very well even without good ratings. The sports bars, beverage companies and plenty of other businesses make a good deal of money from sports so it is a natural for them to target this segment of the radio audience. What is elusive is that while a tiny percentage listens, the chances are they are almost always the consumers of products that market themselves heavily via sports, so while that might be a small percentage of a larger group, chances are almost all of the sports talk consumers are users of the advertised products.
The same philosophy goes for Business talk. The numbers might look miserable but they are very heavy users of the typical advertised products on Business Radio. So while maybe 1% of a popular station might seek a financial consultant, that percentage of the small Business Talk audience might reach 75% utilizing financial consultants, maybe higher. When you compare numbers based on those percentages, it is a no-brainer to choose the low rated Business Talk format for the greatest results.
Needless to say, these are cheap formats to execute, mostly satellite delivered and sales tend not to be ratings driven but rather niche targeted advertising. As a result, a station hitting a 1 with a format on AM would likely have fewer advertisers and less income than a Sports Talk or Business Radio format that either doesn't show in the ratings or maybe only gets a .1.
The hard cold truth is it boils down to money over ratings no matter if it is a Sports Talk or music format. Like any other business, the dollar rules, and in some cases the number of dollars is not tied to the overall ratings. Also, keep in mind the ratings only give an overall picture. A Sports Talk station with low ratings can have a very substantial number of desirable listeners in a certain demographic. I heard one Sports Talk in one market was #1 in men 25 to 34. That's the sort of thing ad agencies pay attention to when their client wants men ages 25 through 34.