As irritating as it sounds, I think it is ingrained in the company's culture that they produce artistic interpretations of pop culture icons rather than focus on accuracy. This can really be seen in licenses such as Gi Joe and He-Man where they design products that have veered away from the most established look of characters even though most collectors would probably rather want collectibles that are close to the source material. Considering the amount of source material in existence for Star Wars, there really isn't any reason to not get things pretty accurate, except that Sideshow is probably allowing design team members to go with what they "feel" is right rather than asking them to adhere to accuracy.
I also think that, unlike Hot Toys, Sisdehow really isn't in the business of fixing flaws in their products after they have been approved by Lucasfilm. There aren't many examples of them doing so.
Hasbro was limited by resources they would allocate for a cheap 1/6 figure. Sideshow is limited by philosophy.