The films had to explain why (or how?) the dino breeding was [intended to be] controlled, and so we knew. The game doesn't need that distinction. The whole its based on the movies isn't a very strong reasoning; if it was, we'd definitely have Aquatic & Avian species because they were in the movies too.Apart from the fact that I'm not very versed in biology, so I don't know if that's a possibility (then again, when did the movies ever take actual science really seriously?), you could ask the same question about the movies. They started out with female only so I'm ok with them sticking with it for the game, considering it's based on the movies.
If you're releasing a game with breeding dynamics, then the addition of male or female makes sense - even if the male ratio is stupidly rare, but to release a game where breeding is irrelevant cause it doesn't happen, there doesn't seem any actual reason to adamantly state "they're all girls". This further promotes an issue (relating to the films) where we know some islands do have male Dinos - we're exploring all the islands in the game, but none of them feature male dinos?