The majority of the one million legal immigrants to the US each year, come based on having a relative here, rather than the skills or wealth they bring with them. That is chain migration - one comes, who brings their relatives, they bring their relatives, etc., in an endless chain.
Rich, well educated, young adult immigrants contribute the most to the economy. Chain migration brings in lots of older, less skilled and poorer people.
As an example, an Afghan Interpreter is given an immigration visa, in recognition of his dangerous service in war. He brings his wife, and has three kids. When he gets citizenship in five years, He brings his parents, and his wife brings her parents. Their parents bring all their remaining children under 21 with them. Six years after a single visa is issued, 17 new immigrants are in the USA. Many are old, sick and unable to speak English. Some are not even literate in their own language. Every five years when immigrants get naturalized, they can sponsor another wave of relatives.
Merit-based immigration, that most countries on Earth use, and which the USA used prior to 1965, prioritizes those who can contribute the most to this country. Family visas are limited to spouse and children.
Sen Ted Kennedy was instrumental in getting that law changed in 1965 and opened the floodgates for illegals to come here.-Tom