I think this is because Freitas and Drexler and others who might have pursued clanking replicators became concerned with nanotechnology instead. It seems to me that clanking replicators are much easier, because we already have all the tools and components to build them (screwdrivers, electic motors, microchips, etc.). Nanotechnology, while incorporating the same ideas, is far less feasible and may be seen as a red herring that has cost us 30 years of progress in self-replicating machines. Clanking replicators are also much less dangerous, because it is much easier to pull the plug or throw in a wrench when something goes wrong.