Some just overstayed. Some were brought by coyotes and sold to factories and growers. The way to stop the latter is to remove the illegality (so that workers can leave their bondage) or at least inform them that they are entitled to a visa when trafficked, which is the law and which is a felony, for the traffickers and purchasers and to get rid of right to work.  Until them, like I said, the Dems will keep counting Latino votes.