Except that could easily be achieved by making the phone slightly thicker, instead. When phones are so thin and fragile that a rigid case is practically mandatory, I don't know why "thin" is a selling point.
We could solve two problems at once: get rid of a camera bump and make the battery bigger at the same time by using the extra space of the camera bump to house a bigger battery.
Not sure why it hasn't happened yet or if it has I don't know if it.
My guess is the same reason glossy screens won out over matte screens for laptops: because they look slightly better on the showroom floor, despite the worse real-world performance.
