This has a lot to do with trying to avoid breaking immersion with oddly-shaped equipment for the purposes of the action being depicted in the cinematic sequence.
Imagine a scene where our protagonist attempts to coerce a confession out of the villain. She draws her weapon and holds it up against the villain’s throat in a threatening manner while the camera zooms in to get a close-up shot in profile between our protagonist and villain. Seems simple enough, right?
Clearly, the positioning of the weapon in this cinematic sequence would need to be very different if the protagonist is primarily a dagger wielder compared to a sword. You can’t hold a dagger and a sword in the same position to threaten - if your sword point were at the enemy’s neck, holding a dagger at the same position would put the dagger’s point laughably far away. If you held a sword where the dagger point would be at the villain’s throat, your blade would already be penetrating through the opponent’s neck. This gets worse the more kinds of weapons we support, especially if the weapon doesn’t have a blade - axe, spear, staff, bow, fist, gun, two-handed sword, mace, club, one-handed sword, crossbow, etc. will all have very different contexts when held to a throat.
In such situations, creating a different animation for this one cinematic for each type of weapon we allow results in a combinatoric explosion unless we severely limit the scope of the weapons somehow. This is why Dragon Age II utilized the famous “murder knife” for many of its cinematics - it was a reliable well-defined weapon that could be used by any protagonist class and still made visual sense. Similar constraints also exist for outfits and equipment. That profile shot would look really weird if, for example, the protagonist was wearing massive World of Warcraft-style shoulder pads that obstructed the view because they was emitting massive screen-obscuring particle effects. We have to standardize certain things in order to keep the scope of the cinematics from ballooning out of control.
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