Or maybe people don't know about the look until after they've upgraded? The Software Update page on the device doesn't show any screenshots, it doesn't even say anything about the new look.
Additionally, there are lots of apps which only work on iOS 7, so often enough you don't have a choice.
Even people that otherwise like the iOS 7 look will admit that a lot of the stock app icons look like shit. Safari and mail and settings in particular are a bad joke.
