How so?
We're not talking love here, we're talking sex. And in this conditions straight people want opposite sex, not somewhat-opposite gender. Same for gay people. There are exceptions, yes, but those are rare.
Mind you, I'm not against bisexual people, but denying existence of sexual expectations is stupid (and this exact situation is why people call the game PC).
Returning to the topic of the game, I feel that this situation is more due to an early state of development. Afterall, genital and gender-related surprises and misunderstandings are a great inspiration for interesting sexy content, from basic "wow, benis" to sexuality broadening arks.