The problem comes when you sit down to work on the next update for that game. Suppose you're making that game, you've included an optional male love interest for bisexual players, but you yourself have no attraction to men. When it's time to start writing and rendering, whose scenes are you going to be excited and passionate about finishing? The girl you personally find really hot, who inspired you to start working on a game when you made her model while screwing around with DAZ3D? Or the guy you have no personal interest in and are only including because it seems like other people might? You can include both but if one of them isn't of personal interest to you, it's very likely to get less quality and quantity of work.
Thus the many games I've checked out with fully fleshed out feminization or submission routes and parallel straight or dominant routes comprised of a couple hasty pages and a [In Development!] sign.