In short, for the Greeks the concept of a "female" deity was very different than the concept of a female human; it wasn't a one-to-one comparison. More can be said about gender perceptions in ancient Greek mythology and society if anyone wishes to add further, but in the meantime, here are some older answers you may enjoy:

• Why was one of the Greek Gods of war female, despite Hellenistic culture's patriarchal roots? by /u/JoshoBrouwers.
• How come some of the most important Greek gods were women (Athena, Artemis, Demeter) yet their society remained so strictly patriarchal? by /u/mythoplokos, which also led to a follow-up in:
• Several ancient polytheistic religions (like in Greece or Egypt) included female deities responsible for areas, that were traditionally men's jobs in the respective cultures (warfare, hunting, etc). How did deities like Athena for instance come to be? by /u/UndercoverClassicist.

Providing some past answers:

• a user (since deleted) sheds some light on the subject by looking at the roots of Greek mythology.

• user Labrydian provides a bit more context to the origins, providing a couple other alternate theories, though the rest of their answer relates more to how fertility is often tied to female deities

• user QVCatullus posits that a few Greek deities, being virgins, in a way reject the presumed femininity of the role of mother

• user jelvinjs7 compiles a few additional answers relating to this, which haven't been included above, that examine the idea that humans and deities are two separate entities

User mythoplokos provides a succinct explanation in one of the above's linked posts:

You could answer this question really briefly: in all simplicity, gods were a category completely distinct from humans. Performing things that humans cannot perform is exactly the whole point of gods; it marks them as non-human. You wouldn't ask why didn't Greek men go around throwing lightning bolts just like Zeus, right? Well, because, rather obviously men cannot control lightning. Similarly, the Greeks would not think that just because Artemis hunts or Athena wears military gear, this is something that women should or could do as well.

Hope that helps!