No one seems to have mentioned, so far, that there are a lot of businesses, BIG ones even, that love cheap labor.
Have watched it since the early 60's when our family moved to SoCal. Prosecutions of those who hire illegals rarely happens, even when BP/ICE/la Migra makes a raid on a business. The same business multiple times even.
Supply and demand............business demands cheap labor and the immigrants fill that demand.