They are using America as a relief valve for themselves.
Years ago, probably around the 1980s, when I first started paying attention to the illegal immigrant issue, the term "pressure valve" was in fairly common use. Meaning that illegal immigration to the US was a pressure valve to prevent any serious build-up of social unrest or revolution in the Latino nations from Mexico on southward.
Rarely see "pressure valve" any more as it's now politically incorrect..