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.
Because they’re probably doing ok, and they don’t want to think about how much is out of their control, and how easily they could be in the same situation.
The idea that success is just down to hard work is comforting, because they think “if I just keep working hard then I’ll be ok”. They don’t have to come to terms with it being taken away. It also lets them not feel any guilt or have to spend time thinking about the problems of others.
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.