Well probably reason is, because it is, people from allover the world want to go to America.
People from all the world, send the American company's billions of dollars each week (Apple, Amazon, Google, Facebook and many more)
Lol! Who said that? USA is one of the most dangerous countries for the foreigners considering the number of crimes happening there every single day! People want to flock to US just because of money but not for peace most certainly! That doesn't make them the greatest country on earth.
Are you aware of the "Global Peace Index 2020"? You can get it from the below link,
http://visionofhumanity.org/app/uploads/2020/06/GPI_2020_web.pdfAs per this index, United States of America stands at 121 in Global Peace Index. There are hell lot of African countries that are way ahead of USA in peace index. In money becomes everything for you, you can stay even in the most hostile territory of the world. But if you want to have a great life, USA shouldn't come within the consideration.
Apologies for deviating from the main topic, but I thought it is necessary to reply!