It was just that their luck was not very good; or more accurately, it was extremely terrible. The legendary treasure was nowhere to be found; that island was actually just a natural trap full of ferocious beasts and deadly pitfalls.
Conversely, on the way back, their ship encountered a fierce sea storm. Waves as high as mountains of water crashed down on their heads, the mainmast was snapped in half by the wind, and they nearly capsized and lost their lives in the middle of the cold, vast ocean.
After enduring great difficulty to survive the storm thanks to the crew's rich sailing experience, they unluckily encountered a giant sea monster attack that damaged the hull. Water flooded into the cabin, and ultimately they were forced to dock at the nearest port belonging to the Catthalan Empire for emergency repairs if they didn't want to sink.
