According to flat-Earthers, the shape of Earth is a flat circle. In the center is the north pole in the Arctic Ocean and Antarctica is not a continent, but instead an ice perimeter surrounding the ‘flat Earth.’
The problem is that there are people who visited Antarctica, and their information about Antarctica does not fit the flat Earth narration. To ‘deal with the problem,’ they invented conspiracy theory and assumed every person who claimed to have visited Antarctica is a part of the grand conspiracy; and they spread the information to deceive us. This way, flat-Earthers’ narration about Antarctica is no longer falsifiable. If something stands against them, their ‘solution’ is merely to add more people to the list of persons that are part of the grand conspiracy.
The existence of the Antarctic Treaty System is convenient. Flat-Earthers use it to support their narration.