If you are a mother making near minimum wage (which, these days, is around $15 in most major metros, regardless of what the actual law is), and you need to be on the job site for 8 hours/day, you're barely if even covering the cost of child care plus commuting and other job related costs. And as a tradeoff you get to have the stress of the job plus the joy of having someone else raise your kids. It just doesn't make sense.

Also, importantly, your Earned Income Tax Credit will be reduced if you make more money (not 1-1, but just another reason why working in a low paying job doesn't really make sense if you have children and a spouse/partner that can support your family).