At the same time, they allow ~1 million mostly non-whites to legally immigrate every year.

I think insurance/medical industry lobbying is a far more consistent explanation. In general, if a story starts by bringing up racism from 150 years ago, it's more concerned with building a narrative than with explaining the current state of affairs.

Rather refreshingly, the NYT admits this: "It aims to reframe the country’s history, understanding 1619 as our true founding, and placing the consequences of slavery and the contributions of black Americans at the very center of the story we tell ourselves about who we are."