Because small races are a pain in the ass to do the cinematic dialogue style. When you are rigging these things You have to try to match up the characters line of sights and fool the player into that the models are actually looking at eachother. When there is a substantial hight difference its mush more work to do this
Go look at karlach talking to her dwarf friend in the panel from hell, it was all just zoom ins on each of their faces. When you have an orgin character, with all the contend that entails, making them short makes things exponentially harder.
Since we can play short races, they have to make the camera work for short races anyway. It wouldn't be any/much extra work. Thoroughly dissapointed at not having a dwarf/halfling/gnome companion.
