Because most people have basic limitations for who they’re willing to accept/connect/make sex with. Most people tend to be heterosexual, so they’re only going to go with male/female pairings and that’s the only gender pairing they’re going to look at. Other people are going to be more open-minded, or were born with different preferences, and going outside traditional societal norms is fine for them. I don’t think there’s anything wrong with either viewpoint, it’s ok to have personal preferences and to have limitations about who you’re comfortable getting intimate with. We frame attraction based on our personal preferences.

So, no, I’m personally not attracted to literally every single female on the planet, but women are my personal preference/limitation, I’m only attracted to females. As a hetero male, there’s just no other way to frame my attraction, that’s just what it is. HOWEVER, there’s a vast array of other orientations out there where that sort of binary attraction doesn’t make sense and is probably counter-productive. I think that’s why we see so many different expressions of sexuality now, because people see the limitations that come from the mainstream male/female model and it can’t be used to properly explain their preferences.