The annual US GDP per capita is $55,036. For Somalia, it's $145

This is availability bias. There are clearly other factors differentiating Somalia and the US. If there weren't, there would be massive starvation in Somalia because you can't get by on $145 a year in the US.

I can assure you that successful people are not born in the US by chance.

Really? Do you think successful people don't have children? And that they don't try to make these children US citizens by 'immigrating' (often illegally) to the USA? I can assure you this happens frequently.

As of 2005, there were 2.6 billion people who lived on the equivalent of under $2 per day

Yes, but most of those people live in areas where $2 goes a long way.

What possible values could they have where that could be considered success?

That's up for them to define, not for you to define. Why should they care about your standards? Let them say they are successful if they believe they are successful. You lose nothing but your ego by acknowledging somebody else's success.