How would they do it? You get Smaugs personality because he has a long chat with Bilbo. So....we need to encounter and chat with him...or have more cutscenes?
Also I believe he didn't have an awesome presence in previous Blizzard games like Arthas had in WC3.
To me, Classic didn't have much of a main Antagonist. Ofc everyone seemed to know KT, Archimonde and Illidan in TBC and Arthas was just perfect for LK.
"It’s not the job of the artist to give the audience what the audience wants. If the audience knew what they needed, then they wouldn’t be the audience. They would be the artists. It is the job of artists to give the audience what they need."
— Alan Moore