Immortality Bisexuality: Might look that way (well, not for the galari, who have no concept of sex, or sex, or gender), but it’s actually the result of desire control, etc., as listed under Bi The Way and Everyone Is Bi. The rest of the immortals weren’t inclined this way until the tech came along to make it so.
(And, to be clear, in many civilized areas such outcomes are desirable. Preferences are one thing, but instincts that contradict your conscious desires on this point are inhibiting your freedom of choice, and as such are instincts that need to be told to shut up and sit down.)
Bi the Way: Actually, pretty common. While the original distribution of sexualities along the Kinsey scale (for the eldrae) would have been pretty close to that found in humans, the brain modifications done under the general category of “xenophobia elimination” seem to have compressed the scale at both ends a little as a side-effect, leading to something resembling this trope although still slanted statistically to one side (since the original curve wasn’t exactly a bell curve).
Not a side-effect that anyone was terribly bothered about, inasmuch as local attitudes tend much more towards “exclusive sexuality is a statistical curiosity, but…” or “ah, you Terrans and your quaint little categories” rather than “your sexual orientation is a DEFINING FACTOR OF YOUR ENTIRE LIFE”. And, hey, more freedom of choice!
(See also Everyone Is Bi for where further individual modification tends to go, sexuality-wise – further down the timeline.)
Everyone Is Bi: Or at least can be, thanks to advances in sophotechnology making gender identity and sexual orientation as editable as any other mental properties, and reinstantiation in general making actual sex changes not all that much more complicated than flipping a few switches in the preferences screen of your brain. And are, in fact, not merely readily changeable, but entirely optional. But yes, most people have explored at least some of the implied possibilities.