I tried asking my mom her reasoning, it was all personal and due to the fact that she wanted a 'perfect family' to have with my dad. It took her 11 years to get pregnant with my sister, who was intentional, however I wasn't. She thought I was the flu for the first while. I was an accident by every mean that they didn't plan for, and according to my mom, everything went downhill after I was born, her marriage, her health, my dad's alcoholism.
She's told me before she wishes I wasn't born for my sake, and the state of my mind.
It took her multiple surgeries and medications to get pregnant, but when she did have kids she treated them so poorly anyway. I still don't understand her reasoning outside of idealizing the perfect "family dream."