Ironically, it is the least used drainage basin of the South American continent. More outflow and more length is good ... up until certain point. And the Amazon River far exceeds the optimal gains. There is simply so much water in the basin that it disturbs the idea of putting bridges or anything over the river. The river is so massive and with a heavy rainforest nearby that using it for commercial purposes for industrial usage is hard. Channeling it for agriculture is also not useful because there is so much rain in the region that the floodplain is not fertile due to extreme natural leaching, making it useless.

You would think that having a bigger river would develop the region more, but the Amazon region is the least economically developed in Brazil, and most countries with rivers that drain into the Amazon River have also failed to economically develop.