Traditional designs are in wood. These are proven designs. They are designed to take advantage of the properties of wood. Making them in other materials is possible but not always worth the effort. The bending properties of wood help build a vessel of good form.
Wood is a fine building material in terms of strength and weight.
Good craft can be made from wood with simple tools. Wood boats are very pleasing to the eye and to the touch. Boats made from other materials require extra effort if they are to appear more than merely mechanical. A significant objection to the use of wood is its high cost and the difficulty of obtaining good wood. If abundant, cheap boatbuilding wood of high quality were available, other methods would be even less attractive than they are now.