well, regards parents feeling they have no choice but to both work, because of mortgage/car(s) etc.... I would think that in the majority that's through lack of thinking longterm at the time of setting up said lifestyle.
As an example, I recently advised my little sister, who's 26 and househunting with her other half, to forego the enormous mortgage and palatial manor they are searching for at the moment as DINKs and consider what they can afford on one salary.
EIther one of their salaries. Mother or father, it does not matter.
I think one issue is that as dual-income-no-kids happy young thing it's easy to forget that down the line, if it's the 4bed garden/garage family home you are buying for the future children, well then, you'd better sort out the finances so that it is condusive to actual, pleasant, non-killing-yourself-family life.
In the case of my sister, this is exactly what they are doing. Oooh, we want a big house as we want to get married and have children some point soon, and therefore looking at mortgage payments they can pay back in their current situation (two Cambridge-graduated engineers working for big multi-nationals- i.e., plenty of cash ) In that situation they will never be able to afford for one of them to give up work.
Sensible and long term financial and family planning is what should be taught to school girls/boys if we are trying to help people be happier later in life, IM humble O.