tl;dr
I want to know why people use flat bars. Just tell us why you like your flat bars if you use them.

Rambling reasoning:

Flat bars, especially riser bars, are popular among the freestyle fixed gear crowd. And, admittedly, they don't look half bad. However, I can't for the life of me put together a reason for them other than bar spins. Are there any other reasons?

I ask this because I see them on so many builds riding around the city. The female bike messenger interviewed on CNN in another thread on BFSSFG sports a set. This makes even less sense for her to do, in my opinion.

Flat bars are meant to be held with a palm-down grip. This gives riders what I call "chicken wing." Many of them stick out their elbows as they ride. If you drop your arms to your side, palm against your thighs, that is the orientation our wrist naturally makes with our arm. If you then raise your arms in front of you, your palms will be facing each other. If you rotate your palms downward, your elbows will naturally want to stick out. You can, of course, tuck them in, but this is less ergonomic.

The hoods on a set of drop bars with brakes or bullhorns at shoulder width allow for a grip which is more natural, more ergonomic. Bullhorns have been getting pretty popular, but they don't seem to have overtaken flat bars. Drop bars with hoods are less common due to the trend of riding brakeless (I won't get into that issue here). However, drop bars with hoods make more sense to me as you have more options for hand position, but if you never use those options than bullhorns are also nice. Also, bullhorns and drops come in widths that are equal to your hips, so they can weave through traffic just as easily while offering better ergonomics.

So, I'm having trouble understanding why you would choose to put on a set of flat bars if you aren't going to be doing bar spins. If you're doing bar spins, I don't question you, you make sense to me. But why that messenger girl on CNN was using a flat bar seems silly to me. If she's a professional who likes to fly through the city, shouldn't she be on bullhorns or, better yet, drops?

If you're going to say that it's all about aesthetics, could you please explain what you think looks better about them? My rationalization is that they are more simple in appearance than the other options. Is it minimalism at work here?

Thanks for your time.