they have different because real money, you can buy immediately you want. But in bitcoin you can gain more money than you have now, and you can buy many things even it is expensive. That the purpose of bitcoin you have your chance to have an big money.
They are created for the to give convenience to the people but real money is more popular as it was first created and supported by the government.
Our real money has no sort of investment features unlike bitcoin where it can also be an investment, for a normal people who's not good in exploring online they'll always prefer using paper money as they are afraid of taking risk, still majority of the worlds population who are using real money has no idea about bitcoin and they might find it as a scam.