How do even people who're mediocre do great in USA?

I am assuming that you are in Nepal. I might be wrong. When you judge that people are doing well, you are judging from the perspective of a Nepali mindset. In Nepal there are not enough opportunities to make money and have a decent life. Most people go through hardship and it's difficult to fulfil their basic needs.

So when you see people going to the US and having a decent life you think they are doing great. The thing is - mediocre in the US is great in Nepal.

For example even if you work at a minimum wage job, you can rent an apartment, possibly pay for car and buy a TV quickly with one month salary. While in Nepal, you cannot do all that. So I think it's because of the minimum wage rule that people in America can easily have a mediocre life, which is considered great in Nepal by most people - and most people are struggling because they can't find a job that pays enough to sustain that kind of life. Maybe 5 to 10 percent of Nepali population have that mediocre lifestyle like in US perhaps less than that.