Because we bitcoins today are assets, still far from being a currency. Most of our commodities today will still be traded will dollars, not with bitcoins.
For me the reason why i keep converting bitcoin because i want to have money for my needs because in my country cash is needed to buy a things and etc.and this is the reason why i join in bitcoin to fulfil my dreams and i think only bitcoin can help me to have an income and it has a big profit that can make us want to invest in it.and converting is needed for changing bitcoin into cash.