Paradox of Choice. Give someone a list of blank traits, and they'll faithfully fill them in, and others will look at them. Give someone an empty box and the word "description," and it'll be a whole lot of empty, or filled with things no one ever reads.
A character sheet should contain relevant information. If a physical description of the character is relevant, there should be room on a character sheet to accommodate that. A character sheet that doesn't have room for that is a game that doesn't care that much about character description. Which can be fine -- not everybody gives a fig what color eyes your elf has. But especially for new players, bits of description like that can help anchor the reality of the character. "Oh, she's got purple eyes, I wonder how that looks with her chocolate skin and bright red hair?"