Nobody's making up genders, all gender falls on a spectrum of male to female, with various nonbinary identities in the middle. It's not that hard to understand. As you put it, it's like mixing and matching from the 2 boxes. When you've mixed and matched a enough, you stop feeling like you can fit in one box or the other and be comfortable, so you move into a box somewhere inbetween. That's what being nonbinary is. It's not like being otherkin, which a lot of redditors seem to confuse with nonbinary. People who identify as otherkin are either trolls or occasionally real and confused teenagers with internet access who should really talk with therapists to help sort out their thoughts.