The Mexican government is perfectly happy just the way it is.  Their receipts of out-of-the-country money (remittances)  exceeds the billions per year they get selling their oil.  $24.8 billion in remittances and only $23.4 billion in oil revenues. 

And the Mexican government doesn't have to provide any services to those workers whatsoever.   The oil revenue requires investment and maintenance.  

 http://www.foxnews.com/world/2016/02/02/mexico-remittances-nearly-248b-in-2015-topping-oil-income.html