Women do productive things that are harder to account for in standard GDP metrics. Does GDP count the implied value of rearing a child? The years of care that go into motherhood? Does GDP go up $40 when a mom teaches a young child some words for an hour? It would if it was a tutor but it doesn't when it's just a parent.
The frame of "women earn less than men" is used to implicitly degrade the life choices of women. I personally just learned that a friend's mom is a foster mother. That is an incredible level of generosity that is outside of my comprehension. Is her being a foster mother worthless because it isn't in wage statistics? She earns a modest income by accounting standards, but the actual value she creates is much higher. Should we tell her to learn to code instead?