Immigration is not based entirely on charity.
https://www.wikihow.com/Immigrate-In...es-Permanently
The history behind family based immigration and how immigration works is pretty interesting.
If you do some genealogy and find out about your ancestry you might find out that the places they came from are not so nice either. Nobody emigrates because there is too much opportunity.
You can find some basics on Wikepedia and move on from there.
https://en.wikipedia.org/wiki/Histor..._United_States