All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Husband-wife relationship has a noble goal, which is preserving our species on the face of earth to worship Allah and settle in therein, as Ordained By Allah. Childbearing is totally shouldered by the woman in terms of pregnancy, lactation, education, and care until the child becomes an upstanding member of the community. It was once said: "Behind every great man, there is a great woman." Based on all of this, how could a woman fulfill her duties to the fullest and earn a living at the same time?! For the sake of justice, the husband was entrusted with earning income to pay for the expenses of his wife and children, and the wife was entrusted with taking care of the children on a full-time basis.
People who have contradicted this divine natural law resorted to one of two things: First: Recruitment of foreign domestic servants, and it is known how horrible they are when it comes to raising children. Second: Birth-control or childlessness, which led to population decline in some countries. This is along with the concomitant spread of vice and sexual chaos and subsequent incurable diseases.
It is true that some woman may not get married, however, if a woman has a sufficient share in the inheritance, then it helps her live decently. If not, then it is permissible for her to look for a decent job to make a living. And Allah The Almighty Knows Best.