Generally they don’t impact the reproduction rate enough.
Let’s take reproductive cycles as an example of there being no single benefit or negative. Some species reproduce in mass quantities and that works for them, while others are slower. The fast one having genes that slow reproduction would probably die out because their adaptation of mass reproduction is what keeps them around. A slower reproducing species won’t necessarily benefit from higher rates as they might overpopulate their range. So what looks like a detriment could just be a thing that neither benefits nor is a detriment depending on the complex context of the species and where they live.
And sometimes detriment are offset by other benefits, like sickle cell anemia having some terrible outcomes but it also protects against malaria so in the context of somewhere with a high rate of malaria it is beneficial to survive to a reproductive age, which would explain it sticking around.