What is that makes the United States such an attractive place to immigrate to for people whose skill sets could take them almost anywhere in the world? (In other words, why is that successive sessions of Congress can basically count on lots of people desiring to live in the United States, thus setting up an environment in which immigration regulation is restrictive rather than open?) (I'm genuinely curious about this…
That is a broad question.
Probably because unlike most other countries, we're a nation of immigrants, and while our policies may not be perfect, we have empathy for people who want to move here, and work hard for a better life.