Many do it out of necessity, but there are also many who take on the additonal effort because they enjoy the challenge and stimulation of the work environment. Not too many men expand their part in the homemaking role for the challenge and stimulation, although more and more do share the chores. Society has not fully accomodated the role of women in the workplace and the military faces many problems of integrating women into the armed forces. Measures such as maternity leave do have a cost and job relocation of one partner presents real problems for the other working partner. In all of nature, the biological role places extra demands on the female of the species.
Women are no exception and none of the changes in our society are going to fully change that.
Marriage and family are always going to restrict the options of many women even as the glass ceiling shows its cracks. However, women's horizons are ever so much broader than they were in days of old. World War II gave millions of American women a new challenge, an income of their own, and a reliance on their own resouces they had never known. They never turned back. Of couse, this disposable income attracted the tobacco interests.