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.)