Porque Drogon não estava em Meereen quando ela decidiu encadear os outros dois dragões e seu paradeiro exato onde era desconhecido.
Following Daenerys' conquest of Meereen, Drogon, who is now the size of a small ship, kills and eats the goats of a local goatherd. (...)
Dany is later dismayed to learn that Drogon has killed the daughter of a goatherd. She tearfully confines the two smaller dragons to the catacombs of the pyramid while Drogon remains at large, having last been seen over the Black Cliffs.
Daenerys confides in Daario Naharis that she has no idea where Drogon has flown off to.
Drogon não é menos perigoso que seus irmãos, ele é o mais perigoso:
He is the largest and most aggressive of the three hatchlings.