Jet engine turbines are wonderfully simple machines when you look at a schematic, but that belies a remarkable underlying complexity. The blades have an intricate shape of complex curves that are hard to manufacture and must stand up to incredible temperatures, pressures, and hot corrosive gases. Even the fan blades of a modern jet engine, which have an easier time of it, are incredibly difficult to manufacture.
Traditionally, fan blades have been made out of metal, but these have their limitations. Composite materials seem a promising alternative, but GE says that even though composite blades are lighter and more durable than metal blades, they need to be thicker.