There are records of attempts splashed across EU material but not much that clearly answers this (and those examples make the 'why not' worse, tbh). My unresearched assumption is that it is prohibitively difficult to properly clone a force sensitive being, especially at scale, as compared to a 'mundane' one. It would seem the force is extremely fastidious and is not a reliable thing to select and induce, not without very concentrated meddling. And the Sith learned in the long run how well that turns out.