The most important one is we can only use bitcoin at online like an online business, online transaction, online trading, online gambling and not all people are using bitcoin. In the other hand, all people use real money/fiat and already known of it. We also can use real money for anything and all people are accept it.
Why you think real money is fiat and not bitcoin ? Bitcoin is a money in itself and it is real money. Only the form of money is changed from physical to Digitial.Currently bitcoin is not acceptable everywhere thats why we need to convert bitcoin into local currency, but in near future when bitcoin will be everywhere available, then we even dont need to convert bitcoins to local cash.