I have found that the belief in genderless Gods mainly stems from the belief that gender is a social construct. But this is not a universally accurate statement.
Gender roles can be a social construct, but biological sex is not. No one gives you that except for nature, and nature is of the Gods, and therefore, defining sex comes from the Gods, not just for humans, but mostly every living thing on the planet. Male and female exist abundantly in the universe, everywhere around us, and also in the Gods as logic would therefore dictate.
Even if you change your sex, you are still defined by that new sex, otherwise why feel the need to change it to better define yourself? And while it's true that we can possess traits from both sexes, we will still have a central manifestation. Sex is a defining characteristic of who someone is.
The gender roles of human society are not what determine the genders or sexes of the Gods in any case. Often, a God or Goddess did not choose a realm because of their gender. Athena isn't the Patron of Athens because She's female, but because She won it. Poseidon isn't the God of the sea because He's male, but because He chose it.
And sometimes, the gender roles of Greek society were the opposite of the Gods' stations. For example, men did most of the hunting, yet Artemis is the hunting and wilderness Deity mainly. Yes, She can have a counterpart (Her brother Apollon) but that even more so proves that the Gods have genders, otherwise why is there a distinct male and female here? If gender didn't matter, why the need for the recognition of two opposites?
Furthermore, the Sex Goddess is female even though men were the dominant sex. The Deity of agriculture is female even though men did most of the field work. It could go on with examples. In a society dominated by men, you would think that the highest stations would go to Gods if gender roles made the determination. But they don't, because Gods are not created by humans. The Gods simply are.
Even if we go back to the gender roles of Greek society alone, we cannot logically argue that those were the only manifestations of biological sex. The Greeks even had certain festivals and religious functions only for women because they were directly tied to being female and not male.
I think the insistence on genderless Gods is really a social construct in and of itself, that desires to remold the Gods to conform with modern social mindsets, but what we have to realize is that such a thing is not necessary, nor do we as humans have any right to redefine a God.
In the Goodness of the Gods, I'll see you at the next Herm down the road,
Chris Aldridge.