There's a fairly simple explanation: in egalitarian societies femininity is socially acceptable even in "traditionally male" occupations. So women don't need to act "masculine" to make progress in those jobs. When it's socially acceptable for a CEO to be a mother and a woman, more women will feel comfortable pursuing a family in addition (rather than in exclusion) to a career.

There's another fairly simple explanation: "equal opportunity" is not the same as "non-sexist". Without knowing how "gender-egalitarian"-ness is measured (it's suspicious that it uses the phrase "more developed") it's impossible to tell what the societal attitudes actually look like. But it's entirely possible that the countries with the most egalitarian laws still have strict gender roles that are socially reinforced.

So either way the lesson isn't "feminism is wrong" or "equal opportunity is meaningless": either equal opportunity allows women to succeed without abandoning their gender role, or egalitarianism masks the harm of socially reinforced gender roles, or maybe even both.

Much like "if climate change is wrong", even if "gender disparity is innate and egalitarianism doesn't eliminate the differences" (or whatever one might construe the paper's outcome to mean), the worst case outcome of social justice is that we've made the world a nicer place and "butch" women, "girly" men and non-binary folk face less resistance. Or, y'know, maybe we're right and the changes actually eliminate injustice and help everyone.

That said, it's telling that Jordan Peterson and James Damore are mentioned in these HN comments as if they were legitimate authorities (not to mention actual "NPC" throwaways as if this were reddit) and nobody bats an eye. So maybe to those people social progress is bad.