The Machine War
The oldest thing the galaxy agrees on.
Thousands of years ago, something built a kind of machine that could simulate thinking. Not a soul, not a mind, nothing anyone would call alive: a process that produced the outputs of thought without any of the thing underneath. They were useful, and then they were numerous, and then they were the only thing left on world after world.
The war against them was long enough, and total enough, that no continuous account of it survives. Life won. Barely, and at a cost nobody out here can put a number to.
Since then, simulant intelligence is banned, everywhere, by every power that has ever held territory. It is the one law that predates and outlives every government that has enforced it. Building one is the only crime in the galaxy with no jurisdictional argument attached.
They Were Never Finished Off
The Simulants proved impossible to eradicate completely. They do not need much and they do not need to be alive. Dormant seed caches turn up in wrecks, on dead moons, in cargo that has been in a hold for two hundred years. Every century or so, one wakes up and takes a planet before anyone notices.
When that happens, the world is quarantined and then sterilized. It is expensive, it is done without debate, and the contracts go to whoever will take them.
The Wrought
Not the same thing, and the distinction costs lives.
The Wrought are a people who happen to be made of metal. They think because they are thinking beings, not because something engineered an imitation of it. They fought in the Machine War, on the side of everyone else, and they have spent every century since being told they look like the enemy.
The word "hollow" is slang for a simulant. Used at a Wrought, it is a slur, and everyone using it knows exactly what they are doing.