People will only consider using Bitcoin as a mainstream currency when it is completely accepted in the financial market. Currently, the coin is banned from so many countries which is not great for being a currency.
Also, the coin is currently too volatile to be a mainstream currency and hence is not a trustworthy exchange means. The coin has to be more stable for the people to do so.
Right now, the coin is a great investment asset to earn good profit returns but is not fit to be a currency.