"Remittances are essentially a tax-free transfer of wealth out of the U.S. by foreign born workers. Approximately $20 billion of Mexican remittances each year [$24 billion in 2014] disappear from the U.S. economy via the institutionalized money transfer industry (banks, credit unions, post offices, money transfer operators, individual businesses, and chain stores), never to return. While this massive amount may be considered virtual foreign aid, it is a non-sanctioned transfer of wealth that is based on a fundamental violation of America’s immigration and employment laws."
The carelessness of multiple U.S. administrations has allowed their home governments to do nothing about their conditions at home--it's a big chunk of their GDP. In resources, minerals, and labor force, they are very wealthy countries.