When I say this, I mean it kindly, and my apologies if it reads as anything else:
It's not an attack on nonbinary people, or on you. I would hope that's comparatively evident.
It's a natural default of how the game presents itself. The light stars, by design, are more female-presenting, while the dark stars are, by design, more male presenting (insofar as any of them "present" as anything to begin with). Gender unto itself doesn't mean much for them, but it becomes a relatively natural default distinction to just use "she" and "he" for sake of clarity and brevity. By consequence, the characters which read as "they" are going to be the hybrids. It just incidentally happens that most of the hybrids aren't humanoid in nature. Even then, though, there's Duality's fused form, which sure strikes me as being neither male nor female in any traditional sense, and while the fusion has draconic elements, it's also distinctly humanoid.
It's not some sort of attack, it's just the natural inference chain from the game design. Half the time when we're using male/female terminology for these guys we aren't even using it in the traditional sense, just by nature of what the starfolk are.
If it bothers you that deeply, then make some characters to spice it up. Make some more humanoid hybrids. Make some dark or lightfolk ocs to your preference. Worldbuild an AU that works differently.
Other people's inferences from the game design and their personal story telling are not an attack on you or on anything. It's just how someone chose to run with the worldbuilding. That's the joy of AUs, you can interpret things as you want and have fun with them as you want.
Plus, most of the gendering that's happening is also being applied to beast-like things. Edda, Aven, and maybe Dark Paladin are the only properly humanoid starfolk. Everything else is some flavor of Critter. Heck, there's a demon and an angel. And legs. One of the "girls" is a six-armed headless Creature. One of the "boys" is a plant. "Male" and "female" are being used more like a different sort of taxonomic grouping here, and in a sense are just synonymous with "darkfolk" and "lightfolk". Plus, from a purely semantic standpoint, it's just easier and clearer and more efficient.
In short, I'm sorry that you feel so stung by this. I'm not sorry that any given person's particular interpretation or flavor of worldbuilding doesn't happen to cater to your desires, because that's just fandom. But I am sorry that you feel hurt. I would encourage you to enjoy and discuss your own take on the story and include in it what you would like to see.
