If you offer Kanta a degraded nanoforge, she'll (or rather, Cydonia will) essentially respond with "Pssh, anyone can find one of those just lying around. It's all but worthless!". This is underscored by the fact that everyone else who might want one seems to have one, from the Luddics to the eternal underdogs at Nova Maxios.
It is worth noting that Kanta will install a pristine nanoforge at Kapteyn if one is given to her, so that's certainly where she'd put a nanoforge, if she had one. Given that the outer sector is crawling with pirates, you'd think one would have brought her a nanoforge at some point.
Of course, the Doylist explanation is the same reason Umbra does not have a fullerine spool for us to vibe check away from them. If a pirate planet had a desirable item that could be taken to immediately reduce the quality of pirate fleets everywhere, that'd be the first stop on every player's list, even ignoring the fact that the sale value of said item is less than that of the supplies that could be grabbed with a similar number of marines, simply because it's (relatively) unique, and the pirates are an enemy that the player generally wants to inflict permanent damage on.
That said, the Watsonian explanation gets trickier. Kapteyn Starworks being an Achilles' heel seems to be an in-universe truth, such that the player is regularly offered missions to knock it out for a little while as a means of teaching new players the economic and military usefulness of disabling a faction's heavy industry, creating shortages and crippling their fleets. If it's regularly raided, wouldn't they pursue an alternative solution (and wouldn't the people running the raids do something more permanent to it, like the player can, given the benefits of crippling piracy sector-wide)? It's hard to think of a level of raiding that would make keeping a nanoforge on hand non-viable but wouldn't encourage the pirates to spread out their production a little. Likewise, if it's safe enough for a pristine nanoforge to be put there if the pirates get one, why not a degraded one? Is it just that a pristine nanoforge would improve their defenses enough that they're no longer worried about raids?