For example, I live in Romania. The net minimum wage here is around 2700 lei, and many jobs (especially entry-level ones) pay that amount or close to it. The cheapest rent in the city is about 1500 lei per month. You literally can’t survive on the remaining 1200 lei. Sex workers are judged harshly, but for me it’s the only job that allows me to live comfortably while also having time to focus on university, especially since my parents can’t support me financially because they are poor themselves.
The just-world fallacy - the belief that the world is fundamentally fair and people deserve their circumstances. People who lucked out in life tend to believe this for the reasons you said.