Question

why conventional current flows from positive to negative

Answer 1

This was the convention chosen during the discovery of electricity. They were wrong! Electron Flow is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source. Both Conventional Current and Electron Flow are used.

Answer 2

currentindependent of the type of charge carriers, conventional current is defined as moving in the same direction as the positive charge flow. So, in metals where the charge carriers (electrons) are negative,conventional current is in the opposite direction as the electrons