Western cultures are still much more understanding of men being absent from their children's early lives than mothers. These sorts of cultural expectations and allowances are often taken for granted by the people who argue that "inequality of outcome != inequality of opportunity."
If women are to take a career hit for raising their kids, why shouldn't the men who fathered them take that hit as well?
I actually thought Sweden already had this, but apparently not. At least not perfectly so, the parents have 480 days in total, with 90 earmarked to each: https://sweden.se/quickfact/parental-leave/
a) Society places a greater burden on women than men for child-rearing. b) Women who take leave lose out on career opportunities. c) Men receive greater opportunities to advance their careers relative to women, since they are expected to take less leave.
Even in the presence of equal parental leave, men (or just as often, their employers) can lean on the social expectation to return to work sooner, disadvantaging women.
This becomes a bit of a chicken-and-egg problem since the culture and structure are mutually reinforcing. From a policy perspective, structure is easier to change than culture. In my view, that makes it a logical first step.