because digital currency is decentralized, the government can get their hands controlling it which makes them quite useless while paper money are easy to track, totally backed by the government so they can do what they want with it: printing, holding, tracking,... If the government decides to incorporate with digital currency, there will be nothing good as they will try to alter it and control it. Furthermore, they still don't really love bitcoin so why the hell do they want to create one and use it? So paper money are still going to be the trend for a while