If the SCL crews were limited to just MIA-SCL, it would be hard for all of them to get in enough hours. The South American (BOG, EZE, LIM, SCL) crews generally fly anywhere in South and Central America, although there are certain restrictions attached to certain flights (SJO is supposed to be APFA only, EZE and GIG are supposed to be split according to a certain formula, etc.).

Actually, what's more surprising is that the crew was entirely SCL-based. The unions that represent the South American bases don't have an APFA-style rule that requires their flights to be staffed only be one union, so you'll often find at least two bases working the South American-staffed flights that aren't from/to the base cities (BOG, EZE, LIM, SCL).

You can see the SCL-based crew's union website at www.stcaa.cl (complete with humorous photos and a copy of their contract).