Since the Alchemist Association took over the former Divine City Nalune, the association's prestige has been greatly enhanced globally.
This prestige, of course, was built on the backbone of the Church, inevitably leading to the Church's exclusion. Without any decisions from the Church's upper echelons, many local churches instinctively began rejecting items produced by the Alchemist Association.
For example, the clergy consciously avoided using Alchemy Items.
This has created an atmosphere within the Church—if you, as clergy, use Alchemy Items, do you think the Alchemist Association is right? And if you think the Alchemist Association is right, you are definitely a traitor... Such an ambiance gradually spread within the Church, to the point where anyone hoping to advance well within the Church would actively avoid suspicion.
Thus, this atmosphere gradually became an unwritten rule.