I think capitalists just want cheap labor. The US itself doesn’t have a unified position on population. Plenty of people want a population decrease because they feel everything is overcrowded.
It's interesting how the sides flipped. Left was strongly anti-immigration because it saw it as a tool of capitalism to drive down wages and just general abuse of working-class rights. Now Left is pro-immigration, and the right is against for the same reason the Left was. When did this change happen?
Well, when I say "US" I mean the current administration and the people that have power within it. Maybe that's not their actual intention or desire, but that is the story their policies and actions are telling.