Evolution is likely selecting for, eg, people who have children at a certain ratio of introverted-extroverted.
Introverted, disagreeable, high-contentious types make, for example, great scientists. A population (call it A) that produces a reasonable number of such people is at a huge advantage compared to the alternative that only produces extroverted agreeable types (call them B).
Population B will be more competitive at breeding, but population A will win any conflict with B because they'll have a bunch of weirdos in the back room producing a lot of high quality science (a classic stereotype with some foundation in truth).
Note that men are much more likely (something like 4x) to be "completely homosexual" compared to women [0]. I'm betting this is because having a few men who opt out of the race to pass on their genes and focus on other stuff is a massive advantage to the society that hosts them. Look how much of a force gay men have been in culture for example.
Locally catastrophic for breeding, globally optimal for society. The equilibrium isn't for all offspring to maximise their chance of breeding. The optimum is for the community to thrive.
[0] https://en.wikipedia.org/wiki/Demographics_of_sexual_orienta...