Introduction to electronic and conventional current:

The direction of flow of electrons gives the direction of electronic current. The electrons flow from the negative terminal of the battery towards the positive terminal of the battery across the circuit as indicated by the black arrow.

Initially, atoms were thought to be made up of protons and neutrons. The concept of flow of electrons came at a later stage. The positively charged holes were considered to be the charge carriers. So the direction of conventional current was considered to be from the positive terminal of the battery to the negative terminal of the battery across the circuit. This is indicated in the diagram with red colour arrow.

Answer:

As many physics concepts, earlier, was explained with conventional current, it was decided as a standard practise to follow and use the concept of conventional current. This is why, the flow of conventional current is in practise even today.