Not only Americans, all settlers in a history would choose to settle by the river rather than in some hills, unless there are special reasons for this, such as the relief of a particular country, i.e. geographical conditions, otherwise, if there are possibilities, the settlements along the river provide a number of advantages. Namely, the rivers provide a fertile soil suitable for processing and rich yields, life in the plain, that is, by the river, it is easier because of the land and river traffic, which again promotes trade, transport, more accessible markets, etc. It is easier to build buildings, houses, factories, and it is easier to organize life in such conditions. One of the reasons for answer specifically this question if it goes back to historical settlement, might be that the Americans rather settled by the river, in order to avoid possible conflicts with Native Americans as if they were settled elsewhere, say hills or forests. Although should not be prejudiced that Native Americans liked the hills and forests, perhaps they lived along the river before the inhabitants.