Find a Guatemalan illegal alien and ask him. Mexico likes to shot what comes across their southern border.
They sure as h**l don't give them drivers licenses, in state tuition at public universities, medical and other social benefits or (Not sure about this one) automatic citizenship to the offspring of Illegals that are born in Mexico.
By the same token I doubt they release them on their own recognizance to appear for an immigration hearing several months later. My understanding is they are locked up in Mexican jails and summarily deported. I'm sure the experience of jail is a significant deterrent to recidivism!