Why is most of North America part of the Atlantic Basin?

This is due to the fact that the western coastline of North America is bounded by the Cordillera Mountains, and there is little area to the west of them for the formation of large rivers. In addition, the western coast is drier. In contrast, the eastern (Atlantic) part is more humid, and the fact that the Caribbean Sea deepens into the mainland makes the southern lands of North America subject to moist winds, which infiltrate most of these rivers.