I’m coming at things from a far-left perspective, sorry. I’ll try to translate.
c) The Koch Brothers – Charles Koch in particular, has been the consistent voice for Open Borders for decades.
They want it from a corporate far right libertarian point of view: free movement of workers means free movement of industry means free movement of wages down to low points. (they are pro elimination of minmum wage for that reason too)
I can find you long defenses they made in the past for completely unobstructed open borders they’ve written, right up to around 2015 or 16.
But it became politically unpopular to talk about that idea at all once “The Border” became the Trump issue he wanted to highlight and so they stopped bringing it up.
So that’s the Koch part.
b) both democrats and republicans were perfectly capable of tackling it from Reagan years onwards. They each had power back and forth at various parts of government.
But they all also have their investments in various industries who depend on the labor being cheaper-than-minimum wage like agriculture and housekeeping, etc.
So they never did anything much about it but lip service.
a) The pay rate of undocumented workers is 75 cents to the dollar.
So an $8 /hr job pays $6 /hr to equivalent undocumented worker. That’s a big savings when dealing with hundreds or thousands of workers and most undocumented workers pay their taxes because they believe it’s a path to citizenship – which it isn’t – but they believe it is, and nobody corrects them.
I can pull up tax revenue numbers from them; very significant through the years; cash cow nobody wanted to give up.