One obvious reason is that Millennial women (especially professionals) have not had babies yet.
The effect of taking time of work for children is not immediate, it creates a pay gap for the rest of somebody's career.
If we imagine somebody's pay over their career as an upward sloping line eg.
year 1 40k
year 2 42k
year 3 44k
etc...
When a woman takes 6-24 months of work to have a kid or two then that pauses their pay increases for that time and they are 1-4k worse off than somebody who didn't take time off at all when they get back. Add to that that women do more of the school runs and other caring when they DO return to work...
The effect of taking time of work for children is not immediate, it creates a pay gap for the rest of somebody's career.
If we imagine somebody's pay over their career as an upward sloping line eg.
year 1 40k
year 2 42k
year 3 44k
etc...
When a woman takes 6-24 months of work to have a kid or two then that pauses their pay increases for that time and they are 1-4k worse off than somebody who didn't take time off at all when they get back. Add to that that women do more of the school runs and other caring when they DO return to work...