The article posits that the affluence of a country (not gender equality itself, though correlated) affects how much the economic security that comes with high-p

The article posits that the affluence of a country (not gender equality itself, though correlated) affects how much the economic security that comes with high-paying STEM jobs is an incentive to purse those jobs. That can explain a gradient between countries, and doesn't affect the original, purely gender question either way.