What does it mean when a woman says a guy they're really cool with is just a friend or like a brother?

there has to be a reason why right? because she thinks you're too nice, gay, she doesn't feel if she puts her self out there you'll take her for what ever reason( a guy looks to good for her, she might feel she's to ghetto, etc etc), or she might look at you like you're not good enough for whatever reasons( don't look good enough, not established enough, to ghetto, to fat, not educated enough, don't have the enough swag aka charisma etc etc), but it has to be something RIGHT? It just can't be for the sake of it, there has to be some type of logic somewhere behind these lame titles, even if they don't want to admit it right? SO WHATS THE LOGIC IN MOST CASES?