The war was over; Germany had signed the armistice before the German fleet was interned. The reason Rear Admiral von Reuter chose to scuttle was because he’d been informed of the terms of the Treaty of Versailles, requiring the handing over of the fleet the allies. By this time the fleet had been at Scapa Flow for seven months and von reuter had none of the things required for the ships to put to sea, least of all crews; of the 20,000 officers and crew that had sailed into Scapa Flow in November 1918, fewer than 4,500 remained on board by June 1919, the mere skeleton crews required to prevent the ships from sinking.
Besides which, a fleet is not a guerrilla army; it cannot roam the countryside living off the land. Fleets need resupply of vitals and fuel, especially fuel. In 1919 that meant coal and a lot of it or the fleet would very rapidly have become nothing but floating navigation obstacles.
They were also guarded by the Royal Navy’s First Battle Squadron, who would have had several hours warning that the Germans were going to try to make a run, this being the time required to heat the boilers.
Ironically the scuttling of the fleet ended an argument between two of the allies and made things worse for Germany. The intention had been to scrap the German ships, this had resulted in an argument between Britain and the United States as to whose shipyards would profit from the scrapping of the German fleet. The revenue raised from the scrapping of the fleet would have been deducted from the reparations demanded of Germany, when the fleet scuttled this very large sum of money went to the bottom of the harbour. Not that that really mattered because the Weimer republic only ever paid a tenth of what was asked of it and dragged that out over fifteen years.