In previous iterations, shaders were dumb. They waited for the CPU to say, "Okay, now render the metal. Okay, now render the skin."
There is a specific sound that unlocks a primal anxiety in modern PC gamers: the whirring of a CPU fan hitting 100% while a progress bar stalls at 12%, accompanied by the text "Compiling Shaders (Iteration 3.0.0)." iteration 3.0.0 shader download
It was efficient for the disk, but terrible for the GPU. You were forcing your graphics card to carry a swiss army knife when it only needed a corkscrew. In previous iterations, shaders were dumb