Probably because the US requested it. A few years ago, Bush and Fox signed a reciprocal fugitive return deal. The US can request Mexico arrest someone wanted here and vice versa. I heard a US marshal discussing this on a radio show in Albuquerque. He said that they had got over 250 people from Mexico in the first few weeks. The idea is to deny criminals the ability to use to border as a safety barrier. Small agreements like this are probably more important than some of the more spectacular agreements.
I wonder why they did that?
Rope-a dope...
Make us think they are doing something.
Neither side wants to fix this