People like to put things into a box, to classify them, make them tangible, to understand at a glance. Thinking of sexuality and identity as a spectrum isn't too complicated. Instead of male or female, you have maybe something ranging from masculine to feminine, and everything in between. But where it gets confusing is how you'd describe either being somewhere on that spectrum, or to what exactly your sexual preferences range. A classical bi person would be right dead center in the middle, or maybe sway a little to one side over the other, but would you still call it bi? Maybe pan? Someone formerly hetero or gay would also be easy, being at the far end of the spectrum. But what about people who are a little more flexible in their attraction? "Girls" with dicks? "Guys" with vags? Maybe they don't even strictly identify as either one. Whether one's more hetero or gay leaning, you'd be likely somewhere halfway towards the middle of your sexual attraction spectrum, just like the people identifying & looking accordingly, but how would you describe that yourself, and others - without being disrespectful for their own identify? Maybe you're gynosexual for the feminine side? Androsexual for the male one? How many people would understand those terms though? "I like girls, including those with a little extra" - "I'm into femininity"? Terminologies are constantly changing rapidly on top of all that too, and for many things there aren't really much established terms either. This further makes it harder for people to move away from the old binary classifications, even if generally supportive in principle. But those who aren't, will obviously just see a very confusing mess of things they don't understand.