Let me add to the Sorrow's post and make it easy to understand.
Even if such model would appear then it would not corelate with other impelmented models. You probably think that character AVATAR itself is a naked figure all the time, and it is clothing that is being changed. Unfortunatelly, that is not the case. Like Sorrow said, it resembles more of a lego than "dress me up Barbie".
Avatar model is separated to: Head, body, hands and legs; means that whenever You chnage clothing on either of those parts, you actually load w whole new model for it. Remember that part. Now... What a texture is, I guess I don't have to explain, but for clarity it is what you see as skin or clothing. Imagine now, that parts of models are made of clay. They already have some default slight colour on them (you can observe in character creator because everything there is set to '0'[don't ask how that work and why it is white]), and they are ready to take a new color from you, but here is the thing, your "paint" is transparent so it captures some color from the clay. Now, all vanilla models (everything that comes from original game) are made of the same clay ergo that's why those model parts will fit with color tone when you choose and glue them together. However, BG uses a moded contnent means that it was made by different people who used slightly different colors of the clay. Now return to the part about Avatars being like lego. You put your model together from different parts, comming from different people and when you paint it, you will get a mixture of tones.
So to put it simple, we would have to take, all textures and unify them so they would all fit together... and honestly that's a s**t load of very frustrating work.

Hope i maanged to explain that in simplistic way.