People who are living on less than 50% of their income (particularly less than half of after-tax income) are a pretty much vanishingly small subset of the population.
It's a smart policy, but it's quite uncommon. When economists think of simplifying assumptions that also help to communicate the essence of a situation, this one doesn't seem that bad to me.
https://www.mrmoneymustache.com/2012/01/13/the-shockingly-si...