To get to USA from either El Salvador or Honduras, you'll need to go through Guatemala and then Mexico. According to the Fragile States Index (
http://fundforpeace.org/fsi/) Guatemala is less stable than both El Salvador and Honduras. So if they're running for their lives from an unstable country, why the fuck are they heading north?
If they head south, they will first get to Nicaragua, which is about as stable as Honduras, and then on to Costa Rica and then Panama, both very stable, comparable to USA. Further, El Salvador, Honduras, Costa Rica and Panama all have something in common... language. These nations are also MUCH closer than USA.
So Costa Rica is closer, safer to get to, and culturally similar. Yet they still travel north.
Why? Economics.