Somehow, along the way, many people lost all compassion. I am really not sure what do they have to gain from being a-holes to genuinely struggling people. (Not everybody wants to change profession at 40-50 and they should not be forced to.)
As you said, nobody who is working full-time should be below the poverty line. Nobody.
But it does show how far we are from getting there when people can't even agree that people with jobs shouldn't be living in poverty.
What's a "livable wage"? The whole point of assessing whether people are "living beyond their means" is precisely to figure out if they're keeping their expenses within that 'livable wage' threshold. I think you'll find that most people with money-related issues ("poverty" in this context should be reserved for actual, true deprivation, which is vanishingly rare in the US! Social exclusion/marginalization is real, but it's a very different problem, with different ways of addressing it) are in fact not doing enough to keep their expenses in check.
https://en.m.wikipedia.org/wiki/Poverty_in_the_United_States
If 12% of your people are living in poverty as defined by your government then there may be something systematically wrong.
Everyone deals with these kinds of intrapersonal conflicts and issues on a different breadth and scale, one way or another. It's this coupled with economic distress or anxiety, in addition to a massive income and wealth inequality, that produces the kind of conditions and struggle that people and families go through, like those described in this short article.
Sure, there are varying degrees of this issue. You have costs of living which vary depending on location, wages and salaries which vary by location as well as the occupation itself.
Despite this, it's still a grave mistake to simply pass many of this off as "they should get a better-paying job" or "they are living beyond their means" as some of the comments on the WaPo article itself suggests.
For the former, anyone who uses such an argument has in some form or fashion accepted the belief that some jobs should not pay a livable wage. It does not make any sense that anyone working a wage job full-time is still financially in poverty. This has nothing to do with the individual, but instead has everything to do with economic policy. That is not to say that, for example, fast food workers should not make as much as teachers. OK, then pay the teachers more. The bottom line is that no one who works a full-time job should be in poverty.
For the latter argument, this is mostly part of an ongoing cultural trend of laying all responsibility on the individual, regardless of systemic variables. The idea that in such an unequal society, where people exist who literally make more in a single day than others in an entire lifetime, we should instead scrutinize the people struggling economically, is just plain disingenuous.
The economy is broken and getting worse. More and more people are realizing it.