“The display is the computer.”
Historically, graphics acceleration started with interpolating colors on each pixel scanline overlapping a triangle and then displaying these values. Including the ability to access image data allowed textures to be applied to surfaces. Adding hardware for interpolating and testing z-depths provided built-in visibility checking. Because of their frequent use, such processes were committed to dedicated hardware to increase performance. More parts of the rendering pipeline, and much more functionality for each, were added in successive generations. Dedicated graphics hardware’s only computational advantage over the CPU is speed, but speed is critical.