If that was done they'd have to rework some of the staves designs. The length and hand position determines how its placed on your back and I know some of them are a bit.... broken? Like they clip into the ground as you hold them in the restoration staff position and other stuff like that. Be neat if they fixed that as well.
I've noticed that as well and something I think about when selecting my staff appearance.
It's also the reason I tend to use 1h swords and daggers because there is no alternative animations for maces and axes for some attacks, like Puncture or Flurry. It just looks silly stabbing someone with a hammer.
It also looks silly sheathing an axe like a sword. All axe holsters I've seen in the real world have the axe blade up and the axe haft falling down the length of the leg.