For me, the fact that a guy is my friend doesn't make him undateable. If anything, if of course I am attracted to him (which can happen), it makes him even more dateable.
But why call it the "friendzone"? It just means that she isn't attracted to him, and since she doesn't want to hurt his feelings by outright saying "I'm not attracted to you", she says that he's "just a friend".When a guy likes a girl but she only sees him as a "NICE GUY", a "FRIEND" and is not attracted in him for dating, he's almost like a brother and it would be gross to date a brother, He's in the "FRIEND ZONE."
It isn't because he is her friend that she doesn't want to date him, it's because she isn't attracted to him and never was.