According to this weighty review of the available data, women in the western world have gotten less happy since the 1970s. In the 1970s women reported being happier than men, but that is no longer true.
The authors of this study offer no explanation for their finding. Now I have to say that I am dubious of this kind of research, which I think records changes in what people think they should say instead of how happy they really are. But to the extent that it is true, I think the explanation is given on page 1 of this study: "Female labor force participation has risen to record levels both absolutely and relative to that of men."
Working more doesn't make most people happier. As the working world becomes more and more a sort of racket in which underlings toil harder for minimal gains while their bosses get obscenely rich, in which employers have no loyalty to their employees or their communities, and in which more and more people do abstract bureaucratic tasks instead of making something, work will more and more become a source of unhappiness.