The vast majority of people in Europe from 1800 to 1900 were poor. Very poor. Those that came to the United States did extremely well, compared to the average European.
The standard of living in the United States today, is still much greater than European standards of living.
Food in Europe costs about 3-4 times the percentage of income it costs in the United States.
But I think the issue is physical beauty. Face it, why would a beautiful, well connected and otherwise highly desirable young woman emigrate to the USA from Europe? We got the hard working, average and so so looking stock.
I had many business trips to mostly Western Europe over the years and on my first I took the weekend to see some sights. I was in Belgium and went to Ghent were I was walking around the city in the early evening and was in the confines of the cathedral (where the Ghent Alter Piece was located). It was an entire village within the walls and as I was walking there was a well-dressed young woman a few yards in front of me pushing a baby stroller. She stopped at one line of the old apartments (inside the cathedral wall) and went in, leaving the door open I looked into a TINY little place that was smaller than my first apartment.
I started to notice how small the living quarters were for nearly everybody, except for the more modern homes located outside of the cities.
Also, buying my meals was terribly expensive all over Europe and it was a relief to actually find a McDonalds. I know I got Per Diem and it always cover my food but not having to pay $35 or $40 for lunch was sure a treat.