I haven't voted on this picture, but I can only assume it's because
it looks like the artist couldn't figure out how to make the pose work with a normal-width chair
the shading isn't great
the shape of her arm (singular, where's the other one?) looks off, and putting it at an almost 90° angle made it more noticeable
the shadows on the floor make it look like the chair is floating (why was the metallic glow applied to the non-metallic wheels?)
It's approved so whatever, and the flaws that you pointed out are rather... small, imho almost non-existant and minusing pictures fo "lulz chair is too wide!" is quite... bad.