Who knows why SS won't book you on the MIA-SCN-MIA flights, which how we went last December/January using their air department. Please note that some of those flights may sell out as a lot of Chileans use them to do holiday shopping in South Florida or to visit with family back home, and we only got business class seats (SS couldn't get them for us) through a combination of having AA status, paying cash and AA miles for the upgrades and a lot of sheer luck.