When and why women left the labour market?
They worked at home. Like "Household Engineers" do today, doing everything working from down to dusk like their husbands, and like their husband they shared in the earnings of the household.
Until the industrial revolution came each household operated like a mini business.  

It was the Industrial revolution that divided "work"(e.g. business) from home.

They never left the workforce, They just stopped being called the workforce.

Ironically with people working from home more and more we are returning to such a system.