Some people DO advocate for better laws. It doesn't mean that it will pass. At then end of the day, you have to convince enough people to vote for people who want to make it a law, or make enough noise and be an enough electoral power that politician wants to do it. But, while a lot of people care about immigration and such, at the end of the day, some other issues (the typical example is the cost of living), might take precedences.

> Also, what makes refugees specifically the US's responsibility? E.g. verifying, processing and integrating refugees puts strain on domestic systems, and strain scales with volume.

I think nobody said it's the U.S responsibility, in spirit. Factually it is by the fact that they have to handle it and international laws. But that is why country sometimes collaborate on those issues. The U.S and Mexico do collaborate on immigration issue. Mexico do stop a lot of south american immigrant from reaching the U.S border. But the border is huge. There is also other ways to get in, legally or illegally. You can't possibly stop everything. And it is the burden you get when you are a rich country. The U.S is not the only one. And mind you, the U.S and Western European country have benefitted a lot from exploiting the people and resources in poor country and pushing allied authoritarian regime there. Immigration is but a small cost they pay for what they did, and got.