Not having children can seem out of the ordinary to some people who then feel they have the right to ask why? This is insensitive to those who may not have been able to have them. When asked why I don't have children my normal response is why do you ask? this often makes people take a step back. Alternatively I have said do you have children, why do you have them? The response I have received is what a strange question, my reply no more strange than asking me why I don't have them.
We all have multiple roles in life, Wife/Partner, Daughter, Sister, Friend, Work Colleague. Being a Mother or not being a Mother does not nor should not define who we are as a person.