HaLeiVi –
You seem to think that the fact that it is not juxtaposed together with Arayos is proof that the Rambam held this is some kind of chok.
While this is an interesting take on it, it is not possible, as the Gemara in Nazir 59 is ???? that it has do with arayos, as the Gemara darshens that when it is a ????? it is assur and when it isn’t it is not.
I would come at it from another angle, with a similar question:
The issur of ????????? ?? ???? is ostensibly primarily an avodah zarah issue. If so, why is it written in the Torah as a preface to the parsha of arayos?
I don’t have an answer but I think there is something to be said along the lines of a lot of the attraction of avodah zarah has to do with arayos and there is a lot of connection between them.