You guys wanna know why?
Well, There is an AOT character that i forgot her/his name but... It's a character who is female in the anime, And male in the manga.
Now. What does this mean? That's right. Scott took it from insperation. Mangle is genderless if this is true. Scott possibly took it from insperation, And made the gender of it genderless. And this was all just to make fans debate.
And this is my theory on why Mangle is genderless. :L