All of the above, and more. In addition to having corporate resources, CBS and Clear Channel also own the top stations in key demos. TIC-FM is routinely top 3 in females and persons demos that are desirable. WRCH is dominant. Over at Clear Channel, they've got a killer combo with WKSS and WWYZ. So with top performing stations and vast resources, CBS and Clear Channel take the bulk of the national ad buys.
So what's left? WMRQ can't pull in the big ad prices because they don't have the ratings. While the top performing stations can pull in serious national ad dollars, stations like WMRQ and WDRC have to rely on more local advertising. There just isn't as much local revenue as there is national revenue. The buys are smaller.
WMRQs expenses are seriously minimal though, so I'd bet nobody's losing money. John Fuller is a brilliant business man. He knows how to make money.