It's Occam's Razor. In particular, nothing else explains why immigration became such a major issue for left-leaning parties around the western world only in the last 15 years: https://www.npr.org/2019/02/19/694804917/democrats-used-to-t.... As it became apparent that immigrants were a deep well of votes for people who wanted to expand the welfare state, immigration--which the left traditionally had viewed through the lens of economics and labor markets--became reframed as a civil rights and moral issue.

But if the dominant immigration flows to the U.S. were like Cubans in Florida (https://www.aljazeera.com/news/longform/2026/8/14/the-party-...), I strongly suspect we would be talking about how wealthy Republicans favor immigrants for cheap labor.