Large cities don't have the sorts of agricultural jobs that illegal immigrants generally work. They also already have high cost of living and housing shortages. So it's not surprising that they have a limited ability to absorb illegal immigrants into their workforce.

Stepping back a moment. We also probably shouldn't be surprised that disorganized mass immigration is causing problems. That's why Democrats generally advocate comprehensive immigration reform. Its going to be easier to absorb immigration if its happening in an orderly manner.