From the article:
The other key circumstance that will reduce the need to emigrate from Central American countries is economic growth. Economist Michael Clemens has shown that as countries get richer, they initially send out more migrants, probably because people simply have the money to move in search of work. But once yearly incomes pass about $7,000 to $8,000 , the effect reverses; opportunities are good enough in the home country that it’s not worth enduring the stress, danger and dislocation of migration.
Mexico is far beyond this peak, which is one reason net migration from Mexico has halted and gone into reverse. The Northern Triangle countries in Central America, however, are all around the level where migration pressure peaks.
