In government funding you ask that they set the money aside for your specific use. So it’s better to get that set aside for as far out as possible so you don’t have to go back to congress every year and risk political machinations. The 12 year funding is likely a 6 year contract with two optional 3 year renewals or one 6 year optional renewal. There may also be a way to move that money into a new program in 6 years more easily than if you had to go back to congress for a totally new budget.