It seems that the only woman the main character has ignored is Mia's grandmother. He has let everyone else pass through himself. How is that possible? What kind of discrimination against old women is this?
He's also ignored Siv the 4th giantess & Makith. My guess is his allure only works on women who are single or unhappy in their relationship. This is of course just head cannon but I have my thoughts. Qetesh is the Goddess of sexual pleasure & ecstacy, but shes also a fertility goddess. For this reason I think she has a hand in what MC finds attractive in a female, specially is she breedable & does she want it?
Greta: Mia's grandmother may be completely past the menopause phase, meaning she has no more egg cells to give children. And she may still hold a flame for her deceased husband. Both things could lead to her not being on MC/Qetesh's radar.
Makith: Again she may be past the Goblin age of menopause & cannot bear more children. She may be an old headstrong Goblin that so strongly believes she is done with her "young" duties that she sees MC as nothing more than her King. That's it to her.
Siv: Might be content, aesexual, lesbian, who knows... she may just not be into MC. She hasn't got a portrait so we can't say if she is also an old woman so I can't be sure about her cycle.
Honorable mention:
Mrs. Miller (as everyone affectionately calls her) might be happy with her husband & content in her life. Also she dosent even have a portrate/only appears in the tavern if MC burnt her house down so it's possible she just isn't on the radar of Tinkerer himslef.