Simply putting a Sports format on an FM station is no easy road to success. In fact, Greater Media's WPEN-FM in Philadelphia is the lowest rated full power FM station in that city. They don't have the Phillies. They don't have the Eagles. And in Detroit, 105.1 won't have the Tigers or Lions.
Sports, done right, is also expensive. First, what network they affiliate with will be irrelevent, ESPN, NBC, Fox. In Market #11, nearly all dayparts except overnights and some weekend hours will have to be local. Are there enough good Sports Talk hosts out there to fill up a schedule? In most cases, you need two hosts because if you're not generating calls, they need each other to talk to. You need call screeners/board ops/producers. You need to have reporters covering the Tigers and Lions every day during their seasons. You need sportscasters to do the updates every 20 minutes. The payroll will have to increase from a few DJs and support staff for a music station to over 30 for a Sports station.
On the other hand, the rewards can be great. Men are valued by advertisers but not as easy to get as women, who might listen to a music station all day. Because it is a Talk format, you can run more spots each hour than a music format without turning off the audience. And it isn't a background format, so the spots are more effective.
Also Sports is the #1 format for African-American men over 35. So that's a plus in Detroit. I wonder how secondary FM Sports stations do in ad revenue? As I said, Greater Media's WPEN-FM has so-so ratings next to CBS's WIP-FM but I suppose it's making money. They sound like they have plenty of spots. They're not running PSAs to fill up the time.
So maybe it's better to be a Sports station with modest ratings than an AC station with modest ratings.