I expect interstates mostly follow the easiest route as did wagon trains, for example “the Whisky trail” that brought Scots Irish from ports in the North south to the end of the Appalachians and train tracks that went from the North around the end of the Appalachians and the west and northwest.
The coastal plain of NC and SC is pretty flat. Ease of acquiring right of way and skirting impediments like small town downtowns and swamps likely dictated the final path of I-95 more than anything else.
The Old Wagon Road into northwestern NC from PA followed indian trails, which themselves followed animal paths. Hilly to occasionally mountainous country.