Typically RPG change character appearance if he changes equipment.
With static appearance, game visuals can be simplified:
Instead of equipment determining appearance, player appearance is fixed at character creation(or enhanced with cosmetic/decorative additions with cash-shop/in-game tuning). Character equipment is only visible to player himself(at equip/trade/inventory pages).
1.Much less graphics to render. Base is static since char creation.
2.Less dynamic changes.(only active weapon-class animations:if class has one weapon type available, also static)
3.provides the solution to looks vs functionality for fashion-oriented players(casuals/female/etc). Players will use best equipment, not one looking cool.