this mostly applies to the U.S. but also most of the western world:
As Marxists we know that most policy is driven by what capital allows or within the increasingly narrow range of acceptable discourse it allows within bourgeois dictatorship
Obviously it's not a conspiracy of ten guys in a secret room but a general consensus that develops from a chaotic web-like oligarchy of money peddlers, influencers, lackeys, billionaire puppetmasters, etc
But this really, really hurts Capital. they need the influx of cheap labor or face the real threat of forced degrowth. and we know every 
including 
is trying to make it harder for people to be childless but short of forcing people to procreate at gunpoint..
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so why allow this to become a bipartisan consensus (U.S.) instead of say throwing some scraps of social democratic programs?
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or in Europe's case allowing these parties to come to power instead of reversing some neoliberal austerity?
Is this a case of anti-immigration just being easier to do vs. building resiliency into the system? i mean it's always easier to write laws crimializing stuff and throwing cops at a problem i suppose
Or something else?
This is my personal belief, but maybe it aligns with reality. Consider where most of these people are coming from. They come from South America, a region that the US has a direct hand in destabilizing. The immigrants coming across the southern border are the product of that destabilization, and they bring with them the stories they have about their life before and why they needed to leave. These stories directly undermine the narrative presented by the state about these people. They need the population to be fearful of them, so they do not allow them to integrate into the community and, as a byproduct, share their stories with that community.
That sits alongside all the other reasons mentioned already. More power to deport immigrants means more leverage in the hands of those who utilize their labor. Those tools allow for a kind of shadow slavery. Illegal Immigrants exist in a kind of superposition of being criminals before being tried as criminals. By existing inside the borders of the state without proper documentation, you are automatically a criminal. The more you restrict immigration laws, the more you make it difficult to legally immigrate into the country, the more likely you are to drive up the actual number of illegals in the country, and force them into this contradiction.
You don't want the public to trust these people in any capacity because they might tell them the harrowing conditions under which they exist, and you might become sympathetic to their cause. So they are "othered" in the same way that minorities throughout history have been "othered" so they can be used as scapegoats for the failings of the state.