This is based solely on my curiosity and I never see it mentioned in any of the relevent posts .
Is it possible that a major factor contributing to the piston failures is that the gearing in the transmission and final drive is too tall and is constantly placing the engine in a load condition which is constant on the engine .
My hilux does seem too tall in its gearing even from take off in first gear . Other 4 cylinder diesel vehicles are noticeably lower geared to intitiate the vehicle momentum .
In a sense if the gearing is too tall then its like driving up hill endlessley , placing a constant additional load on engine internals . Its just a thought and maybe others might be able to add to or expand on this .