The schedules are loaded, but it seems that AA has not released any A inventory on those flights. I did a quick search for a week in December, and there is no A inventory on any flight from USA to EZE/GRU.
Apparently EZE & GRU are some of AA's best performing routes for paid F, so they may just be holding on to those seats in the hope of actually selling them. It does seem a bit unusual though, to have no A available on so many flights, as A is a revenue fare class, though probably not as good as full F.
There is D inventory available on almost all the AA flights, so you could book Business class and keep monitoring for A in the hope that it becomes available nearer to flight time.
Good luck.