Do you need an explanation for why there are dragons when the real world doesn’t have dragons? Because it’s a story. Do you need an explanation for why those dragons can fly when logically a creature of that size shouldn’t be able to do so? Because it’s a story. Do you need an explanation for why a human wiggling their fingers and saying certain words causes lightning to shoot out of them and fry that dragon to a crisp? Because it’s a story. Do you need a reason for why that finger-wiggling human is a gay woman and not a straight man? No, you don’t, because it’s the least absurd thing in this paragraph and you accept all of the others without question.
Heterosexual: Fuck that.
Homosexual: Fuck this.
Bisexual: Fuck you and also you.
Pansexual: Fuck everything.
Demisexual: Fuck you in particular.
Asexual: Fuck no.