Why didn't Bhishma kill Kansa if he was powerful in reality?

Why didn't Bhishma kill Kansa if he was powerful in reality? Because there is no logical reason for Gāṅgéya Bhīṣma to fight or kill Kamsa. Kamsa was never a person who was extremely powerful in the first place. Kamsa did not even have the power to conquer empires or challenge Hastināpura. Kamsa was not an enemy of Hastināpura, hence there was no need for Gāṅgéya Bhīṣma to either fight or slay him. Only a fool would make an enemy out of Hastināpura. Since Kamsa never made an enemy out of Hastināpura, there was no need for Gāṅgéya Bhīṣma to kill him. Gāṅgéya Bhīṣma is way above people like Kamsa. Does India go around attacking their neighbouring countries just because our neighbours are bad to their own citizens?