My tentative hypothesis: the less difference there is, the more important it becomes to signal it. More weird stuff in the article.

Wealth seems like the best explanation, since it empowers self-expression in a general sense. One of the main comparisons I saw focused on comparing Scandinavia and India / China, and asking the women why they went into whatever career they went into. Indian or Chinese women go into STEM fields not because they like them more than alternatives, but because they represent a stable, high-status job or a path to America or so on.* Scandinavian women are happy being nurses because the job is more enjoyable and they're wealthy enough to want a larger share of their compensation in job satisfaction instead of money.

*It's not the thing I read on gender differences, but Peter Chang's story seems interesting and relevant. The government decided that he would go to culinary school, and he wasn't interested, since he wanted to be a scholar, not a chef. His dying grandmother gave him advice to learn any skill at all:

She told her grandson that “you should not just think about yourself, whether you’re happy or not,” Chang recalls. “You have to consider that you’re the eldest son of this family. On your shoulders, there are your parents and your younger siblings, and you have to think for them.”

And then he goes on to become a master chef and gets to America and is now running a chain of restaurants. But the advice seems very un-Scandinavian.