I thought of McCall Smith and the gender issue and I think the unusual aspect is that it's a man writing for a woman, as the reverse happens all the time. There's the Golden Age and Peter Wimsey, Hercule Poirot, Alan Grant and Roderick Alleyn. P.D. James and Ruth Rendell have male detectives. And so forth, even Liam Campbell.
I think that's mostly down to gender issues and having men in the position of power and frankly, what sells best. It's a truism that while little girls might read the Hardy Boys, little boys would almost never read Nancy Drew.