I think there is reason to suppose bisexuals would hide their true sexuality to avoid aversion. Let's be honest here, there are plenty of stories passed around friend circles willing to talk about it about being dumped for men or women from bisexual partners. In mine, it's often so the bisexual can have children, and the homosexual partner was "for fun". If people were honest, these kinds of things can be avoided, but because they're not it's often a cheap heuristic to avoid heartbreak. If you're factoring in possible relationship disaster, removing that additional risk can feel more comfortable - and so bisexuals hide their sexuality to avoid being rejected for that heuristic. Which further reinforces that heuristic when those same bisexuals dump gay men to have relations with women for children. On and on it goes. Of course the solution to all of this would be for everybody to stop lying, a kind of mutual disarmament, and be honest about what they truly want in a relationship -- good luck getting that to happen. Am I saying this doesn't happen otherwise? No. Am I saying bisexuals are liars more than usual? No. Am I implying anything at all about any particular bisexual? No.

So far as populations of attraction go, there are some preliminary psychology studies suggesting that attraction to transsexuals is something of a unique fetish or fascination. The full study is available on PDF here, and wikipedia has a brief summary of it here. This third group is significantly autogynephiliacs (42% self admitted) and bisexual (41%). What needs to happen, however, and what I have not found, is a similar penile measurement reaction study to sanity check self-identified sexuality of supposed "gay" or "heterosexual" men and whether their reported sexuality is misreported for the remainder groups.

As there are more self-reported bisexuals than there are gays or lesbians (surveys differ but bisexuality is usually self-reported as higher or same-sex and opposite-sex contact [bisexual behavior] reported as higher), it's entirely plausible the primary acceptance in terms of attraction and relationship will be from bisexuals.

I am uncertain of the cause behind it, but there are also real relational complications statistically from bisexual relationships. The data I've seen is not clear whether that is in opposite-sex or same-sex relationships, however (except for bisexual women in opposite-sex relationships). Gay men with other gay men have the lowest domestic violence rates, but bisexual couples have the second highest (behind lesbians). It's hard to say as most studies report results by grouping in gay/bisexual together, and without distinguishing them, or only focusing on bisexual women without evaluating reports from bisexual men. This may intersect with transgenders as well, and perhaps everything stems from the same problem. What that problem is, however, is very difficult to determine when researchers continue to use improper and unclear methods or arbitrary groupings that obscure possible correlations.