why is electric current a basic physical quantity???

The electric current is equal to time rate of charge. As such, current is not basic in nature. We could have included “charge” as the basic quantity instead. But, due to other requirements of a fundamental unit like reproducibility and ease of measurement etc, which need to be taken into consideration.

Also, we study electricity as the flow of fundamental electric charges. The historical reason for using electric current as a base unit is that electric current is more easily measured than electric charge.