Great comment, Lexie, the answer is in the breakdown of the statistics, despite some studies showing as many as 30 percent of young women identifying as bisexual, which is crazy higher than the number of men of the same age who do so, when it comes to actual sexual interactions and dating, there are way more men dating and sexually active with each other than women dating and sexually active with each other.
That means when it comes to the LGBT side, the higher number of active men with each other than women, means that the same-sex scene overall gives men more options rather than taking them away.
Why this is, who knows, perhaps women simply identify as bisexual more as a means to please men and their love of lesbian sex rather than out of a desire to actually date women, or perhaps women find finding the right women to date even more difficult than finding the right man, who knows.
Whatever the reasons, the numbers of same-sex relationships and men and women active on these scenes are so small compared to heterosexual, that they don’t make a statistical difference when it comes to explaining competition on the heterosexual dating scene, at least not on the wide level.
Hope that makes sense, thanks for the comment!