I know that material fatigues over time, but 225,000 tons of turbine blades annually sounds excessive. Why so much waste? Couldn't older ones be retro-fitted w

I know that material fatigues over time, but 225,000 tons of turbine blades annually sounds excessive. Why so much waste? Couldn't older ones be retro-fitted with newer rotating internal components to extend the life of the structural components and the blades? I just can't see such a massive structure being discarded just to be replaced with a unit which is probably very similar.