According to the BG3 art book, they softened Lae'zel's appearance to look more human and make her more appealing.
In other words, much like Karlach, Larian made her look more Caucasian because they view that as the only proper standard of beauty and because they associate not being Caucasian with being an evil, stupid savage (i.e. Lae'zel's entire story arc).
