Their are so many reason associated with this topic. Bitcoin is like an e-wallet which is created by blockchain technology  to store and spend by digitally. Bitcoin is much easier and less volatile then real paper currency. Bitcoin is globally accepted easily accessible than cash. Bitcoin is also easily exchangeable with other currency. If someone earn bitcoin then he doesn't need to pay tax but in case of real money you have to pay tax. Bitcoin is the first Decentralized digital currency that doesn't come under any particular person control. But in this real money  it is strictly undercontrol of government.