Because it's bound to come up in the future

The reason there's so much hate for the profile sheets is that it's not given to the reader when they pick up your book and never will be. I could write a 500,000 word essay on my character in a biography and then hand you a book about the guy - you'll have no idea who on earth I'm talking about or where all of these random skills, traits, relationships or character elements are coming from.

You cannot - CANNOT - depend on a profile sheet to tell your story for you. Having one doesn't hurt because it allows you to keep track of who's where doing what, but it tempts you to take certain character elements for granted, turn what should be a passion into an obligation or get distracted by things that aren't relevant.

"Sergeant Johnny Walker cowered beneath what was left of the rotten log as bullets sent flecks of mud and clumps of foliage into the air. The air around him sang a deadly hymn that he didn't really like the sound of because he was more of a Sinatra man like that time back home when he was dating his second girlfriend and she commented on how beautiful his blue eyes were and he got kind of uncomfortable because of his old-fashioned views associating the word "beautiful" with "feminine" which contributed to his poor performance in the bedroom eventually leading to them breaking up after an argument over dinner because he really wasn't fond of the way she cooked peas in the microwave instead of on the stove because that's just not authentic home cooking. And then he got shot in the head because he zoned out and I can't be bothered keeping this guy alive - he was going to die in the next chapter saving a baby anyway."

I'd like you to point out where the writer got distracted and suddenly felt the urge to inject random details from the profile page because they wouldn't get another opportunity to crowbar it in later.

You don't meet someone and instantly know everything about them - hell, most people in real life turn out to be vastly different to what they first appear to be. As the writer - the God, shall we say - your omniscience allows you to dictate exactly what changes are going to occur when and how, but never, EVER insult the reader by giving it to them on a plank of wood scrawled with crayon.

"The big scary biker actually like kittens later on - MEGA PLOT TWIST"

Characters are carefully crafted elements in a story, but the reader never knows this from the onset and never will if you just link them to your character's facebook page.

The community that post on writingforums.org are your audience, so when someone posts a profile page with details as unrelated or obligatory as their date of birth, eye colour and favourite pizza topping, here's what we do as a general rule:

*glance over it*
"Eh... they look interesting... I guess. I can't even remember what I was reading, I zoned out because none of this is being put into any kind of relevant context, it's just a bunch of info about someone I've never met nor cared about."

I cannot stress how uninteresting it is to read a laundry list of character information without any driving force behind it. It's like trying to write an autobiography using bullet points with a 500 word limit - it tells us NOTHING. It really is like receiving an invite on facebook from some random without nothing but a profile picture and the list of their favourite things on their homepage. And unfortunately, pretty much everyone deals with random facebook friend requests in exactly the same way:

Ignore