Each company has their "Mickey Mouse" character, the iconic one that all eyes are on and you just can't mess up. For Lucasfilm, Yoda is that character. It means less creative freedom when designing that character, but sometimes getting it just right is worth the effort. Yoda went through a few more iterations after this, but this was the one where the Lucasfilm guys said "Yeah, that's him." Sometimes as a concept artist, you have to take the small victories however they come.