We're one working parent household with 2 kids. I wouldn't say it was a breeze but definitely not as difficult as some might think. We live comfortably, not pay check to pay check. We own the home we live in and take family vacations at least once a year. We don't splurge on cars but drive decent cars that we keep longer than most families (8-10 years). We cook most of our meals instead of eating out.
We still manage to save for retirement (both 401k & IRA) and build up a rainy day fund. We are also contributing to, with some help of their grandparents, 529 accounts for both of our kids.
Yeah and part of it is just what folks are comfortable with.
I'm looking to fast-track to retirement, so I need dual income to do it. On top of that, I gotta pay for my kid's college because god knows why our government will only give secured loans to people with low income. You might as well have an insurance plan that asks the question "Let's get the most riskiest people and only insure them"