Even when there are female characters, a lot of the time their interactions revolve around men, or are handwaved. I'm thinking specifically of the two kinds of relationships that get slashed most often, rivals and best friends. Even if there are two female best friends in a mixed gender group, their relationship will have little more characterization than "we are girls and we're best friends", which just isn't enough for me to work with. As for rivals, it's rare that female rivalry is portrayed with any depth.