So we know the default iPhone camera app does lots of post processing of the raw data from the sensor lens before capturing its photo. Then why does the “auto” button when viewing a photo back (edit -> auto) it the camera app doesn’t already do this computational photography to make the best photo (brightness / contrast adjustments and so forth)?
I like your question. I think it has a lot to do with user psychology. Users usually do not know what they want, they want an automatic solution without hassle, but at the same time want to feel in control. So Apple gives them a processed image out of camera, and then you can process it a bit more if you want.
That is Apple’s approach to software for many questions, they develop something simply that satisfies 90%+ of users, and if you want something different there are many alternative camera apps in the AppStore.