secondchoice is on the right track; the gulf coast FM dial is so crowded these days it may be impossible to move even a few miles further east to the towers east of Loxley.
That said, it's surprising that iHeart or their predecessors didn't attempt to do that years ago. There are benefits to co-location: the stations could share one antenna, one feedline, have one big transmitter plant at the base of the tower, and probably pay less rent, too. Going to one of the more centrally-located towers would also cost them a good 100 feet of antenna height. Of course the only thing I can see that extra height at that location giving WRKH and WMXC (and WABD) is more usable coverage in Pascagoula and Biloxi. But who knows if that even comes into play with commuters anymore or not. It comes with a tradeoff of a worse signal east of Pensacola. I doubt any of them are usable in Fort Walton Beach, Crestview or Destin, whereas WKSJ and WTKX probably do a lot better there.