In a way, a character sheet is a more organized than an essay. What you would put in an essay is almost the exact same thing you would put in a character sheet. When people look through a character sheet they don't want to read a 5-8 paragraph paper just to look for a line or two bit of info/context about said character. If you wanted more context about their personality there's a section labeled personality for people to quickly get the info they need. In the essay you'd have to skim through it just to find the info needed. If I want to know the age of a PC I'd rather have a small little section like "Age: 33" to just glance at rather read through it trying to find it in a jungle of words.
Besides I'd probably make a character sheet anyways. It's kinda like the prewriting/planning stages one has to do before creating an essay. For myself I need to jot down things for my characters in order to remember them, maybe off to the side or something. If I basically already have all the info I need for my character organized into sections why would I need to go through the hassle of rewriting everything in an essay format?
TL;DR
A character sheet IMO is more organized and is easier to find specific information about a PC.