We don't actually know why it is; we just know that women....
We categorize “full-time”--it's a Statistics Canada construct--as 30 hours or more. That's what we consider to be full-time in the labour force survey, and indeed when we look at the labour market in general. So 30 hours or more is what we call full-time work.
The latest LFS numbers show that in April of this year, a woman worked about 37.9 hours per week and a man worked 43.9 hours per week. That's as of April. Over a period of a year, all of that, of course, adds up. But we don't know why they're working less.