Why was Gulliver put to sea in a small canoe with meager provisions?

In part 3, chapter 1 of Gulliver's Travels our hero sets off on his third voyage. He's heading off to Tonquin, which is in modern-day Vietnam. The captain of the ship has business ashore, so he puts Gulliver in charge of a small boat with a handful of men under him. Unfortunately, it's not too long before the boat is captured by two cutthroat bands of Japanese pirates. Traveling with the pirates is a Dutchman. Gulliver pleads with him to let him go, appealing to the Dutchman as a "brother Christian."
The Dutchman is unmoved by Gulliver's request; in fact, he's so annoyed by his insistent pleading that he advises the Japanese pirates to throw him into the sea. Thankfully for Gulliver, they ignore the vindictive Dutchman and decide to spare his life. They set Gulliver adrift in a small canoe with some meager rations to last him for a few days. No reason is given for why the Japanese pirates grant Gulliver such a reprieve; he merely says that "it was determined that I should be set adrift, in a small canoe, with a paddle and a sail, and four days' provisions."