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?
These people are all in their positions because they do well at progressing within those positions (every organization is a meritocracy under its own twisted definition of merit.). Occasionally somebody gets to the top because they're a genius manipulator with no moral compass who will just do whatever lets them win (Bill Gates) but most of them get there under qualifications like "guy who allocates capital towards things that happen to be profitable in 2000-2020 and who started with at least a few million dollars" (Elon Musk). In all parts of the web, people who can be described as "guy who does thing that happens to progress in this role" outnumber "guy who does whatever it takes to advance, which happens to be this thing."
The complex web you describe doesn't actually support capitalism inherently, it's just that:
People with power (who are mostly top capitalists) try to steer the system towards their benefit. Most of them don't know what they're doing and steer it in random directions. But the ones who do know what they're doing aren't fighting each other as much, and it usually drifts their way.
If the system as a whole fails to navigate material constraints and/or account for the majority of power blocks, it collapses. Remaining systems are those that have not collapsed.
The inertia from 1&2 means that the system will generally at least do something that would have worked 20 years ago.
So to your question, there's not a deep supply of people with power that know that anti-immigrant policy will harm the capital class in the long run, but there is a deep supply of people who have advanced through the pundit/lackey system by riling up anti immigrant sentiment, and will continue to do so, because they're best described as "guy who riles up anti immigrant sentiment and benefited in an environment where that happened to be beneficial" instead of "cunning manipulator who rode anti immigrant sentiment to power". The richest person in the world is also currently a dumbass and happens to be anti-immigrant. And the system has not faced a crisis of shooting itself in the foot with anti-immigrant sentiment in the last 20 years, so it does not have inertia-based protections against this sort of failure.