Right now it is still necessary to convert digital currencies into fiat. It is still necessary because there are things that bitcoin itself or other coins can't buy. What is the other option then? Convert bitcoin into fiat money in order to buy things that can't buy using crypto coins.
Cryptocurrency has been accepted in some countries in the world but not all are accepting it or they don't even know it so they prefer fiat money rather than crypto
The reason why bitcoin cannot buy most of these things is just mainly because it is hard to find merchants to accept them so far. I would really want to see the time when merchants will start making good use of bitcoin as payment system in flexible terms as this would really create huge awareness for the currency. However, I believe this would obviously mean the government one way will have to be involved.