They have no prospects at home because they aren't allowed to have them. Not all --- because Mexico is doing some big people-dumping --- but many do just fine when given half a chance. Many of those hated Indians and Mestisos are far more clever than Mexico's elite and middle classes are --- far quicker at figuring things out --- but that's the result of a social system that ensures that all good jobs can only be had by connections.
Many of those hated Indians and Mestisos are far more clever than Mexico's elite and middle class. Uh... most middle-class people are "mestizo" though that word really hasn't had any meaning since the early 19th century.