It’s simple. There’s an intense extra pressure for women in STEM fields – particularly in mathematics – to succeed. That has psychological effects.
At present, while men also have pressure for success, there is not an extra societal pressure for men to succeed right now in these subjects.
As there was an unreasonable discrepancy between women and men in these already high pressure exams who otherwise were similar in abilities, something had to be tried. There was clearly an invisible handicap.
With this minor change, test scores for women in these maths tests improved.
Would there be a similar increase in men’s scores with the extra time? I don’t know if they tested that.