Do they issue such cards in Mexico? I'm not sure why anyone would get one there.
They only issue those cards in Mexico, as I understand it, but perhaps their consulate offices issue them as well. As to why someone would get one, it should be obvious. They either live in the US illegally, or plan to do so, and need/want a document to be able to open a bank account, rent an apartment, etc, and then come across the border illegally, as so many thousands do each year.