There are exceptions like kids and chronic health issues but most people could save a lot more money if they wanted.
I say this without judgment, people just have different priorities. I recognize my advantages, but I have more savings than most people in my family, despite probably having the lowest lifetime income.
Someone who graduated in 2005 will often have a completely different experience from someone who graduated in 2008 or 2009. People who haven't had to look for a job since the '80s are especially befuddled to learn "ask for the manager" leads to "there's an online application kiosk by the door, go there." Usually along with "we don't have any openings, but we keep it on file for 6 months!"
Another thread on HN helpfully has examples of people refusing to go along with it. I don't think they're representative.
This sounds impossible, unless maybe you’re not counting all spending as “ordinary costs”?
If you look at all the categories that are "non-ordinary" because most people spend no money on them, they are pretty obviously lifestyle flexes. For example, if you blow your entire paycheck on a bar tab, that is not classified as an ordinary expense because most people don't do that.
Subtract the median ordinary expense from the median income, you are left with more than $12,000 per year as a surplus. This is called "discretionary income", money you can spend on fun, hobbies, or -- relevant to this thread -- savings. If we restricted it even further to ordinary and essential spending, the income level that no longer generates any surplus is in the region of 15th percentile IIRC. That is still 20 million households in the US with no ability to save but that isn't the experience of the vast majority of households.
The Bureau of Labor Statistics and the Federal Reserve publishes surprisingly detailed statics of what people spend money on and how income surpluses are used.