In our world, it is reasonable to say that the more skillfully an item is crafted, the better its quality becomes. A suit made by an expert tailor is higher quality than a mass-produced suit of the same cut. Similarly, you might expect that a sword forged by a master blacksmith would be much stronger than a blade forged by an amateur.
This fundamental principle of the universe is different in Animus.
In Animus, an item's quality does not depend on how well it is crafted. In Animus, an item's quality is ultimately determined by how well that item is taught its purpose.
As items are used they are instilled with purpose, becoming better at what they do.
This happens to all items gradually.
Items which survive long enough tend to get more powerful.