Ok, but then why can't these devices "assemble" limpets or Modular Terminals?
Our limpets *might* also be flat packed for space-efficiency, and hence are already assembled. They're at least several metres long, aren't they? Can't imagine there being room for 500 of them in my hold! Who is to say that the controller doesn't put the kits together for us?
Remember that FD haven't told us we make the fighters from dirt or materials: We need 'ammo'. ie the flat pack kits.
As to modular terminals, there is a big difference between making a robot to assemble a flat-pack piece of furniture and it being able to make printed circuitry from raw materials. Assembling means that you have a kit to assemble from.
And that is putting aside ideas like copyright, DRM and intellectual property. 'Modular Terminals' are probably a proprietary part, and in societies which still cling on to property and IP laws, the patterns for them would not be available and the standard assembly machines would be firmaware locked in a manner that proprietary parts can't just be photocopied.
There's also the quality element: I want Modular Terminals for a crucial part of my spaceship. Why would I use a patterned part, knocked up in a high-tech photocopier? I'm happy for my decoy fighters to be made of cruddy plastic, but would you use a cheap knock-off Chinese gasket in the engine of a racing car, let alone a spaceship?
But The main reason we can't just make modular terminals from dirt is that Elite is not a post-scarcity setting. If you can have a machine in every home that can make modular terminals or whatever you want from dirt and have unlimited fusion energy, then it's a very different sci-fi setting. There is then no need for finished commodity markets, as only raw materials are needed, no reason for us to haul finished products around and no real reason to hang on to outdated ideas like 'money'. Star Trek's Federation and The Culture are both examples of sci-fi societies where 'replicators' exist, and hence, there is no need for money.
I knowledge that the whole concept takes some mental judo to justify lore-wise, and that such lore should have been laid out by FD instead of us having to backwards engineer head-canon, but the tech can be justified.
