EZE is a tricky route in terms of equipment. The overnight flight from the U.S. arrives first thing in the morning; this is similar to a TATL flight but the time difference between IAH and EZE is just a couple of hours, not 6 or 7 like Europe. And this time difference makes a big deal. The return flight from EZE to IAH leaves late at night. Thus, CO leaves a large widebody on the ground in EZE for 12+ hours every day. The one daily non-stop CO flight takes two 767/777 to operate. Adding another flight would entail encumbering two more widebodies (whcih CO does not appear to have) or using one bird but departing and arriving at some strange hours.