Marc Ornstein gives an exhaustive list of why.
I'd only make a slight geographic codicil to this penultimate sentence: "Largely, inland paddlers used canoes of various forms because of their flexibility and adaptability while coastal paddlers used kayaks because of their seaworthiness on open water." In arctic North America and perhaps Europe and Siberia, natives indeed paddled skin kayaks on the ocean, but also paddled open umiaks. In South America, natives used bark, wood and reed open canoes. In the Indian and Pacific Ocean basins, outrigger canoes—which are open canoes—were (and still are) the ocean paddlecrafts.
I'd only make a slight geographic codicil to this penultimate sentence: "Largely, inland paddlers used canoes of various forms because of their flexibility and adaptability while coastal paddlers used kayaks because of their seaworthiness on open water." In arctic North America and perhaps Europe and Siberia, natives indeed paddled skin kayaks on the ocean, but also paddled open umiaks. In South America, natives used bark, wood and reed open canoes. In the Indian and Pacific Ocean basins, outrigger canoes—which are open canoes—were (and still are) the ocean paddlecrafts.