Wheatwine:
It may be that the writer's core fantasies involve being spanked by a person of the opposite gender, or possibly by a person of the same gender. So the parent of the gender not fantasized about is not present, but some explanation for that parent's absence is given. (Death, divorce, travel being part of the job, and so on.)
Whether my underage spankee protagonist is male or female, if he/she is going to be parentally walloped, my clear-cut fantasy preference is that it be by a woman.
I'm usually not even bothered to explain why 'Dad' isn't ever around, or even referred to, but my preference would be that he's "a businessman who travels a great deal." (I don't unnecessarily cause fictional men to suffer death or divorce.) If the guy does show up, it's almost certainly to be embarrassingly chastised by his wife, possibly in front of her girlfriend(s) and/or his daughter(s), or even with her (their) participation in his punishment.
So he may be better off 'on the road,' from that perspective...

--C.K.