Wow, these women are the height of irresponsibility.
Here's my theory about why people think that women are more responsible for birth control.
1. They are more directly affected by pregnancy. They are the ones who would have to bear the child or to have an abortion. Abortions are not fun. Vacuuming your uterus is probably not a pleasant experience. Of course, I'm being somewhat flippant. I do think that women who have foresight and intelligence are responsible human beings who try to have children only when they want to. Of course, there are cultural and socioeconomic issues at play here. I"m not trying to suggest that men are not affected by children, but they don't need to bear the physical consequences. So birth control is more of an abstract conception for men. Although they bear the financial consequences...sometimes.
2. The idea that women are more responsible in general. Of course, this is a terrible and misguided stereotype. I know many irresponsible women (One similar to your story - she has two kids now.)If women seem more responsible, it's probably because society teaches women to be responsible and risk-averse from birth.
EDIT: for grammar and formatting.