The artifact trade finances the Corsairs, the properties of artifacts are little understood and potentially extremely dangerous, and they could aid the Nomads. The artifact bans wouldn't just be due to Nomad infestation (which I believe is very real and exists beyond Das Wilde in Rheinland, into Liberty and Kusari, and possibly even Bretonia) but due to human concerns, or even Order sympathisers of varying motives (profit, ideological support, war support).