Throughout the entire game, she seems actively disinterested in sexuality and a person's appearance (which factors into sexual attraction, obviously). One notable example is in Pittsburgh, where you can have an optional conversation with her after coming across an advertisement featuring a female model, where she talks about not understanding the point in grooming one's appearance, especially dieting to look nicer. And at many points in the game, she goes on about how it's funny that girl's had to worry about little more than looking nice and finding love before the outbreak happened. Ellie doesn't at any point come off as gay, or come off as straight in the main game. She comes off as actively disinterested in any and all romantic or sexual relations. She seems much more interested in, and in need of, feeling like she has a family she belongs to. Which is why Joel ends up becoming a father figure to her.
Making her gay is tacked on, forced, contradictory to material in the game, and irrelevant to the story they have been setting up, therefore adding nothing to the narrative, making it feel like nothing more than a cheap attention grab than an earnest attempt to add something compelling to the character. Unlike how they handled Bill, which is the real kicker I feel - it wouldn't be as bad if they didn't set themselves a standard with Bill, who is an example of a gay character done right. It didn't require an interview to confirm it because his actions had enough nods to the fact in-game for it to feel like a natural, forgone conclusion after a certain point, and it didn't contradict any of his actions. And it made sense in context because he is a survivor, born well before the apocalypse happened, so he can feasibly grasp the now old and dated concepts of sexuality in this post apocalyptic world.
It tends to happen when you take someone who is overly cold and logical, and have them say things that a much more emotional person doesn't agree with.
This is neither a compliment or an insult towards either party.