This does seem to be an age old discussion among parents, particularly among women with young children.
I can think of various reasons why people can't work:
Just had a baby and breastfeeding
Mental or physical health conditions
Caring responsibilities - e.g. elderly relative
The money does not cover childcare/commute expenses
Personally, I do work (30 hours per week) but I am lucky in that it is shifts around the school so I don't have childcare costs. I would never slate someone who couldn't find something suitable for their needs or pressure them to take something that is going to cause them undue stress because they are put in a position where they are forced to be unreliable, which, frankly, I would be if I were forced to work 9 to 5.