Women have always known when their life could not support a child, either its birth or its nurturing. I think adoption has been with us a long time. However, a woman may not be able to stand that choice. Sometimes, only an abortion will allow the woman to see her way clearly to work and keep her sanity and that is why it is chosen.
They all had different reasons for having an abortion, but all of them thought over the decision very carefully before hand, discussed it with the father and (except in one case) their family. Also when I was in a clinic, accurate information was being given freely about all sorts of family planning options, not just abortion. No one ever tried to actively encourage the women to make one decision or another, and instead were supportive and helpful of every decision.