Why are women less happy now than than they were 50 years ago?

"Relative declines in female happiness have eroded a gender gap in happiness in which women in the 1970s typically reported higher subjective well-being than did men. These declines have continued and a new gender gap is emerging -- one with higher subjective well-being for men."

The above is taken from a study that shows today's woman are actually less happy now than before. Why?
Why are women less happy now than than they were 50 years ago?
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