Question

Why is india, pakistan, bhutan and bangladesh called indian subcontinent

Answer 1

because they were separated from India and before they were included in Indian continent

Answer 2

Once upon a time India,Bhutan,Pakistan and Bangladesh were the part of a single country and they all together covered a large portion of the continent and belonged to one of the most important part of Asia. The place was referred to as the Indus valley and this is why India, Pakistan, Bhutan and Bangladesh are all together referred to as the Indian sub-continent.