There were a few factors that kept the blockade around. A major factor was that keeping the blockade helped keep Germany negotiating with the Allies. Without pressure on Germany, some members of the Allies thought that Germany would back away from negotiations to continue fighting. Another factor was that the Allies wanted to starve Germany. As bad as this sounds, it is true. Since there was a revolution in Germany from November of 1918 until August of the following year, the Allies had the interest of keeping democracy in Germany. The Allies wanted to do everything they could to keep extremists from coming to power in Germany, which happened to be starving the German population. Without food, fighting would eventually stop or at least die down.

If you want to read about these subjects more, I suggest the following websites: www.nationalarchives.gov.uk/pathways/firstworldwar/spotlights/blockade.htm

https://mises.org/library/blockade-and-attempted-starvation-germany

https://libcom.org/history/allied-food-blockade-germany-1918-19-n-p-howard (PDF link on this site)