I'm happy to speculate. I don't know the answer 100%, but in part I'd like to refer back to the earlier question or comment about access to child care.
I think this is actually very important, because when women leave the workforce for a period of time for parental leave, if they aren't able to return in a timely manner or feel they can't find adequate child care, they stay away longer and the gap grows. I think access to really good, high-quality child care is essential. Quebec has nailed it.