Final answer:
Brobdingnag's trading with other lands could be inhibited by the roughness of the water, making it difficult for ships to sail, lack of navigable waterways, prohibitive transportation costs, and internal policies limiting trade.
Step-by-step explanation:
The question relates to the fictional land of Brobdingnag in Jonathan Swift's classic novel “Gulliver's Travels”. The narrative does not provide a comprehensive reason for the lack of trade, but we can infer from similar contexts in literature and history. Factors such as the roughness of the water, which would impede the sailing of ships, and the potential lack of navigable waterways for trade could significantly contribute to Brobdingnag's isolation from trading with other lands. Additionally, prohibitive transportation costs and risks such as piracy along trade routes, as well as possible internal policies limiting trade, could also play a role in restricting Brobdingnag's commerce with the outside world.