One biological "purpose" of an abortion is to allow the parent to invest more resources in preexisting children or to save resources for future children, to reproduce when times are better. Animals do exactly this kind of thing all the time. They don't have as many offspring as they possibly can. Instead, they have as many offspring as they can
successfully raise to maturity. If times are harsh, they put off reproduction until a better time. They even engage in infanticide at times. I'm not promoting that. I'm just saying that there IS a biological imperative to limit reproduction.
This is more obvious in parents that invest a lot into the offspring. In animals where the fathers don't do anything but donate sperm, they tend to try to maximize the number of offspring and also their size. (Fathers that help raise the offspring are less likely to do this.) This results in the father giving genes to the offspring that make the baby take lots of calories from the mother and get very large, and the mother, in turn, passing on genes that minimize these effects, so she can has the resources to raise other offspring and live long enough to raise the one she's carrying, instead of dying...
All of this is well documented in the field of "parental investment."
Parental investment - Wikipedia, the free encyclopedia