It's quite simple, most of the people who are fleeing here for a better life aren't the ones who are successful they are the indigents. They are the ones who are poor and struggling so by Mexico getting rid of these people it gives their economy the best chance to survive. It would be like us working behind the scenes to get our poor and out of work, up to Canada so they'd have to deal with the problem.
Which gets me thinking, why not load up buses of illegal immigrants and give them a free ride up to the Canadian border. Our GDP would go up. Unemployment would go down. We'd be able to create a surplus budget to pay down our debt. I've got to hand it to Mexico, they're pretty smart.