Is it easier or more difficult financially for families to have a stay-at-home parent now as compared to 20 years ago?

The answer is not so straightforward. It depends on what kind of stress level your family can handle and how adept at change are you.
In yesteryears, Fathers were the main/sole breadwinners. They did not handle the affairs of the home too much and mums were there to raise us up.
Today, the majority of the workforce is leaning towards women. This fact is reverse that 70% of investment decisions are made by men.
So you see, today we are in a transition of some sorts.
I don't think the expectation of women for men to provide for them will dissipate. Therefore in a Stay-at-home situation, most likely the parent will be a Stay-at-home mother. But in this transitioning workforce environment, is it still viable? Most likely, the women have an easier task to get and hold onto a job compared to a man as the trend shows.
My answer reflects beyond numbers and figures, rather looking towards societal changes and trends. To have a stay-at-home parent is best for a child but the question remains, can a family bear the consequences of an untrained man from the lack of a stay-at-home father figure or a family with irregular income as jobs are now brittle rice bowls.
These are the challenges we face for our children's upbringing.
As a side effect of the stay-at-home issue, on the corporate level - are we breeding a generation of men that are increasingly verse at politicking at work to hold onto their jobs?