Isn't there unmentioned statue of limitations in those rules like if you ask a question and no one answers and it falls of the front page then it is not likely to get answered so you need to reply to it if you want an answer.
As for the question itself. Is the fact that you can only make one a bug that hasn't been fixed or intentional. If it is intentional then please explain why?
I'd imagine it is intentional. Soul Linker mains have commonly complained about the class being nothing more than a dual client link slave typically. When I frequently saw them, they would either go afk outside of castles, or in emperium rooms until an attack came, and they had to link other players (since there was usually just one).
As a note, this was around a year ago, so I'm sure this has slightly changed albeit probably not by much.If you consider this it'd make more sense. Rather than allow a player to easily make x garments, they have to choose one (short of going through the hassle of making multiple Soul Linkers to have multiple garments). And in scenarios where that choice fails they would have to be more reliant on a fellow Soul Linker and High Priest/Priest for survivability or swap to a less desirable carded garment. Since the class is foremost support, it should stick closely with other support players in a competitive environment and even moreso other Soul Linkers since they function best when they are near each other.
If multiple garments could be made, you'd be taking away from that sense of cooperation. So you can consider it a guided attempt to get Soul Linkers to play more as the class was intended.
It won't completely solve the whole dilemma of SL slaves + the limited class loyalty base, but it slightly addresses it. I'm not certain this is the reason, but it is what came to mind foremost. You could argue against it for various reasons, but you'd get the basic rebuttal: SL is non-trans, so they should be squisher even while boosted (inability to swap SQI garments does this). Additionally, they have plenty of skills that keep them alive. Even more so if the SQI discussion grants them KE.