(for us history) why were tobacco, rice, and indigo plantations more common in areas east of the fall line?

These territories were a piece of the Atlantic Coastal Plain, which gave level land and fruitful soil for developing harvests. Another reason is that waterway freight ships could convey edits downstream to port urban communities on the drift. Freight ships couldn't without much of a stretch travel inland territories upstream of the fall line on account of rapids and waterfalls.