Replicator machines could outlive their creators. Then maybe most civilizations think it's safer not to risk being discovered by one, just in case it exists. That seems reasonable and doable.
Replicator machines “seem doable”?!?
Explain. Seriously. Explain what technologies and energy sources would create a complex autonomous machines from unrefined raw materials.
If it’s easier, explain how you’d make make a paper clip from first principles in the middle of a Greenland glacier. What are you going to do? Use electrolysis to split the water, and then have a fusion device fuse hydrogen into iron? Scrape across the surface to find trace atoms, and hope you find enough iron? Even if you have the iron, are you going smelt it, or what? How do you plan to forge it into steel, and then shape it? Are you going to use a tunneling electron microscope to place individual atoms? What’s the energy budget for this? How are you collecting and storing it? What’s the mass of this machine?
At this point, we’re talking about a World Devastator from Star Wars: Dark Empire.
“Seems doable”! Pshaw! EVERY ONE of these thought experiments from the 1940s are just magical premise to base a much simpler analysis on. In the case of Von Neuman proves, it’s determining a limit on how fast you could settle the galaxy. It’s not a serious technical proposal. It never was.
The problem with von Neumann probes isn't the proverbial 3d printer. It's the filament. You have to build an entire supply chain for every individual component from first principles. That's why I asked how do you even make a single paper clip in Greenland. That's literally just a stainless steel wire. That's trivial compared to making an excavator, let alone an interstellar spacecraft.
Think about it. Mineral deposits aren't uniformly distributed. You're going to need to combine elements from thousands of kilometers away, and that's assuming their reachable from the surface with relative ease.
The only plausible way to build a "replicator" is actually to send entire premade factories, harvesters, and transports to a planet in a giant cooperative swarm, along with literally tons of preprocessed materials for repairs until you get a self sustaining supply chain running. And that implicitly assumes that all the requisite materials are even available. Land on a planet without plate tectonics, and your heavier elements may forever be locked under tens of kilometers of solid rock, or even better 60 kilometers of solid ice, liquid water, and rock. (Good luck with your Europan gold mine!)
Oh yeah, and it all of it has to work after a million years in hibernation.