Planes sit there because of the flight schedule, just like foreign carriers have planes sitting in cities all across the USA's big airports. Plus in GRU those mechs do a lot of work, go through the logbook sometime of the 777s that spend time there. Mostly cards are getting accomplished and MELs are being removed, not every station operates like DFW where nothing gets accomplished except for the break room geniuses saying what AA should do. There is only so much room at DWH.
DFW should be broken in two, DFW (terminal operation) and DWH (HGR operation) seems like the management from DWH is much better and will be able utilize all that hangar space so much better, DWH should be able to bring all wide body phase checks to DWH, use the hangar space and have shorter logistic lines along with paying less rent then say in JFK etc etc.....and for an added bonus all 300 plus mechs that want to transfer to texas can transfer to texas, where you would have a motivated work force.