Because, for some of us, a thinner phone is superior in that respect. I work at a desk all day, which means I can easily charge my phone anytime. But I also wear a suit, and thick phones look terrible in suit pockets. A thinner phone makes sense for this use-case: battery life isn't much of an issue, while phone size is an issue. On weekends, if I want, I can use the battery case. Best of both worlds (for me).I get the appeal of a thin phone, but if the battery is bad, why purchase the inferior device? The rumors say that a new battery case will be released alongside the iPhone Air. So, Apple's solution to improve battery life is making it thicker—like the Pro models? I hope I'm wrong, but it doesn't sound right.
I still don't know if I'll buy it. I need an always-on display and a decent camera, and I'm not sure it will have those things. But if it does, I'm interested.