At this point in time there arent many reasons to convince someone to use bitcoin instead of cash. Cash is accepted by virtually everyone, it can be transported short distances physically with almost no hassle, and its an easily graspable concept.
Now I said there arent many reasons, but there are a few big reasons. The first is that bitcoin is decentralized.
Its now a month later. The United States (or your residing country) has been swiftly conquered by an up-and-rising dictator. He sends out an order to all federal banks and the national reserve that the USD (or residing cash) is no longer valuable. The only money that is accepted is now the dictators money, with his face on it.