Why did Louisiana farmers use water to transport goods

Because it was unsafe to travel another way.

In an era prior to the safe roads, all the people used the rivers to transport their goods, since it was much faster and safer than going in carabanas by the desertic roads, and full of bandits; In addition, the country's rivers, such as the Mississippi, the Ohio, the Missouri River, and Illinois, were used as a means of transportation and also to link to man-made canals, such as a waterway, by which farmers in Louisiana and many states found this form of transportation very useful and became so popular that large channels were formed that united important cities such as the Eirie Channel connecting New York to the Atlantic market.