Well it is simply that cash really works offline and it is the traditional way. This is the way of trading where we became dependent to it. Having a cash in real life is the traditional way of living, means that every people used that especially our elders. But bitcoin is the new money or new currency. But I think we need to cope in the future. And this is the future, this is bitcoin. The next generation of currency.
For now most people will prefer cash because it is easier to use than digital currency or bitcoin. Because the environment has not been so supportive using digital currency. If all places are already using and receiving digital currency cash will certainly be dissapear