Various points:
1) No one in Astlan would be making demons out of humans, they KNOW it doesn’t work that way. Demons are primordial beings who are innately evil. You can’t make one.
2) Demon princes often reshape lesser demons in to other forms, other types of demons for their own purposes…this is generally a very Chalkeresque experience and not something one wants to happen.
3) Women often summon Incubae. But remember, Incubae carry the seed of other demons, by default without another demon, they shoot blanks so the woman doesn’t get pregnant…and incubae have other characteristics (long prehensile tongues, funky tails, multiple sets of arms, etc) that make them super lovers. So they make incredible secret lovers behind a husband’s back.
Spoiler: this is basically what’s going on with that shifty, untrustworthy, lying incubus in Book II.