This was partly due to COVID-related tax credits, but even pre-pandemic, the number was around 44%.
I'm not saying this is a bad thing, by the way.
[1] https://www.cnbc.com/2021/08/18/61percent-of-americans-paid-...
https://nomadcapitalist.com/global-citizen/countries-no-inco...
https://www.irs.gov/pub/irs-pdf/i1040tt.pdf
Note that right away, it begins with taxable income. That means you've already subtracted the standard deduction (25k for married couples), and any pretax deductions like 401(k)s or HSAs, which could be up to ~25k, and health insurance premiums.
The current Child Tax Credit is 3600 for children under 6 (3000 for children 6 and over.)
So, based on the above tables, assuming that a married couple can do no better than the standard deduction, and qualifies for no tax credits other than two Child Tax credits, they have to have more than about 63k of taxable income to be paying any federal income tax at all.