Current computers are disposable. If any part ages or fails the entire computer is tossed out. If there were a market for them then someone would produce modular computers with plug-in components. When the processor got old and slow it could be unplugged and replaced. When the hard drive got full another one could be added. There is no need to replace the shell, drives, fan, power supply and connections when one component is broken.
If several universities or state governments banded together and ordered a product down the line then the suppliers would respond.