Why does a current flow from positive to negative?
An electric current is viewed as flow of positive charges from the positive terminal to the negative terminal. This choice of direction is purely conventional.
As on today, we know that electrons are negatively charged and thus, the conventional current flows in the direction opposite to the direction of electron motion.
Also, since electrons move from lower potential to higher potential in an electric field, the current thus flows the opposite and it is easier to visualize current flowing from a higher potential to a lower potential.