[bhaak]

I think I recall some articles about studies that showed that homosexual people (that don't reproduce themselves) are useful as caretakers for close relatives as they want to ensure the survival of similar genes.

Your question is similar to the question why old humans don't just die off when they can't reproduce anymore. This is most obvious with women when they enter menopause but also the quality of sperm declines with men with age.

They are either useful to some extent to reproduction or improving the survival rate of the offspring, or at least the evolutionary pressure is too small to eradicate these traits.

But as we have descended from group animals, I suspect the former.