One reason why is because Americans are more atomised culturally than people from, say, Mexico or Guatamala. Americans believe that you should live independently after you graduate from HS (or else go to college) and don't generally want to live in a home with multiple families or even the same family consisting of multiple generations under a single roof.

Actually, sometimes American real-estate owners won't even rent a unit to more than N people who are not all blood relatives.

Exactly, the question I ask when we talk about sending people back to wherever is "Who's going to pick my lettuce?" Americans don't want these jobs.

Fun story- lettuce picking used to be relatively high skilled and high paying, and the lettuce pickers were the backbone of Cesar Chavez's unionizing. This made them expensive enough that it was worth automating their jobs away. Today, a guy with an extremely fancy tractor does it.

>If it is a question of a living wage, surely, those immigrants who are taking up those jobs are making a "living" with those wages.

Well no, they're not. They are not making what Americans consider a living. You might say Americans have spoiled, overly-high standards, but hey, it's America, so Americans have a right to set their own standards.