The US Chamber of Commerce is our archenemy in this regard. They have been funding court challenges against states like AZ and AL who have implemented tough E-verify laws that were upheld by SCOTUS last year. They want to keep the flow of cheap labor coming. And they have supported amnesty for those already here.
The power and influence of the Chamber cannot be underestimated when it comes to the Rep Establishment and the politicians who depend on their campaign contributions.
Historically, immigration was designed to bring in either the politically oppressed,just a few individuals here,(the blind chinese due for example) or others who can actually fulfill a need the country has.
Mexicon welfare people and pregnant women desiring anchor babies do no fall into that category.