Why do some mothers commit maternal filicide?

Maternal filicide is when a mother murders their child. Clearly, it is a horrible thing that should never occur. But in reality, maternal filicide has occurred several times before. It said in the arcticle "A 2014 Brown University study analyzing 32 years of filicide arrests found there are about 3,000 instances annually in the United States where a parent kills a child." This is an astonishing statistic, and it raises one question. Why would some mothers commit this horrible act of maternal filicide? It also said in the article that mothers killing their children had depression, psychosis, and suicidal thoughts. I would definitely agree with this because to me, it is unthinkable to see a mentally stable mother kill their child. The only way I can see something like this happen is if the mother was mentally unstable. I also believe that stress can cause this mental instability, and if the mother is single, young, and/or poor, she could become mentally unstable and possible commit this terrible act. If the mother has a mental illness, she could be very dangerous to her children. For example, as it said in the article, the mother heard voices telling her to kill her children. I think that if a mother is mentally ill, someone close to the situation should try to find immediate help to prevent something such as maternal filicide from occurring.