Unfortunately many women worldwide, and especially in the developing countries, have no rights and no access to healthcare (ie contraception/safe abortion on demand, like in UK), women there have no choice and are treated as below men, churning kids out year after year. It is just the way it is, i'm sure if they had a choice, they would not choose to have all those children.
Under no circumstances am i saying they should all be entitled to stay here, but you should understand that not all women are lucky to have been born UK citizens.