They are CONSIDERABLY close to Orr. Plus, since some dragons were corrupted by Vizier Khilerbron, who is CORRUPTED . Cantha is nowhere close to Orr. And Khilbron wasn't corrupted, he was just an undead - nor did Khilbron "corrupt dragons" - he turned some dragon corpses into undead. But Cantha was fully unaffected by Khilbron.Khilbron's corpse was IN Orr.