There's a number of reasons for not switching from Windows 7.
First, it's the operating system most of us always wanted. It gets closer to a perfected version of Windows XP. It does everything we need with the software and the interface paradigms we've known for 20 years.
Second, I don't trust any new product until it has been on the market for 18 months in order to get the bugs out. Developers know why, and the reason isn't developers (generally).
Finally, I distrust trends. They blow through, take your money, and blow out the other door. I trust reliability and paradigms that are time-tested.
As a lack of positive reason, I'm not sure what Windows 8 offers that Windows 7 does not. There are improvements; they look really neat. I'd like to play with them, on some computer I'm not using for work when I have lots of spare time to play around with it.
The computer is a tool for me. I use it to achieve other ends. Thus I'm not that fascinated with the OS and want it to "just work." Windows 7 does that, or an adequate job of it at least, on a wide variety of hardware.