how does the Colorado River compare to the Mississippi River? It is cleaner. It is muddier. It is longer. It is more treacherous.

Canyon formation fundamentally requires uplift. This can mean either vertical movement of rock with respect to a fixed reference frame (e.g. sea level) or a drop in the base level to which the river drains. The materials that the river flows over can play a role, with generally more competent (i.e. resistant to erosion) rocks promoting canyon development as steeper walls can be maintained, but without uplift, a canyon will not form. Comparing the Colorado and the Mississippi, the fundamental difference is that the Colorado Plateau, through which the Grand Canyon has incised, has experienced significant uplilft, where as the center of the North American continent is not experiencing significant uplift.

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there are other donors which also make great increases

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The first few sentences mention how the top three donors accounted for contributions, and then the last sentence talks of other countries that made "substantial increases".