Why did the United States put an end to its immigration quota system in the 1960s?

The Immigration and Naturalization Act of 1965, also known as the Hart-Celler Act, abolished an earlier quota system based on national origin and established a new immigration policy based on reuniting immigrant families and attracting skilled labor to the United States. Over the next four decades, the policies put into effect in 1965 would greatly change the demographic makeup of the American population, as immigrants entering the United States under the new legislation came increasingly from countries in Asia, Africa and Latin America, as opposed to Europe.