A child at the wrong time can destroy a mothers life.
The mothers life is important, too. If it was easy to live a single mothers life, getting an education, having a career or just earning money while raising a child. I might listen to you, but currently being a single mother lowers your social status, makes you poor, takes up all of your spare time and then some.
And it is their body and womb, and sometimes that other being is not welcome.