There is a close long-term correlation between low-skill wages and illegal immigration. An influx of low-skilled labor drives down wages at the bottom of the income scale, aggravating the wage gap and social divisions, providing fodder for left wing demonization of the prosperous and successful.
The normal equilibrating capacity of a market economy is short circuited when the influx of low-skill illegal immigrants is nationwide. If American workers could easily escape to another country offering higher wages, then wages in the USA would quickly recover from a surge of immigrant workers, and employers would gain only a short-lived benefit. So, it might not be worth paying off politicians to import cheap labor from poor countries.