Clipping issues and resources.
The only way the DA team could get away with scabbards is if most of the swords were the same shape and sizes. The Witcher, which does have scabbards, is a good example of this. Geralt can have many different weapons with different stats, but they all more or less look the same.
If the DA team were going to have scabbards there could only two basic sword types, with all your one handed swords looking nearly identical except for the hilt and perhaps color, and all your two handed swords also being of the same size and shape.
I'd be okay with that so long as the basic designs looked good, but I'm sure many wouldn't.