There are a whole bunch of ways I can imagine justifying that for different campaign worlds. (Flavor related to various power sources like a blessing/commonly trained magic ability/ki; an ability to just be so awesome with your weapon it's like magic; or a gift from your order or the local royalty).Hell, just an ability at level 11 to ignore resistence and immunity to non magical damage would completely erase the one tiny vestigial need for exactly 1 magic item per purely mundane PC, at most, in cases without party buffs.