Windows 8 "metro" UI caused an uproar for many reasons, some of the biggest ones being:
- the start menu covered the whole screen
- applications could only run full screen, even the simplest ones. You literally couldn't have 2 applications on the screen at the same time.
- it was hard to close applications
- it was very difficult to find the shutdown/reset/etc options
- the metro versions of "default" apps looked bad and were vastly inferior to the "old" versions. A lot of system settings ones had this problem, too (not relevant to the average user, but I use a VPN that is impossible to set up to work in the simple "metro" VPN app, but if you find and start the old win7 app which still exists, you can set it up correctly and you can even connect to it from the "metro" VPN app after that)
- a lot of computer games that worked on 7 didn't work on 8 (likely unrelated to metro UI but still a reason for many people not to update)
Some problems were fixed in Windows 8.1. In Windows 10, most of these things are fine (although Win10 gets hate because of its update system and because it installs unwanted apps, but it seems to have much more acceptance overall).
Windows 8 basically offered nothing to the average user except annoyance so people didn't want to update. It had a very nice improvement for developers in the form of Hyper-V, which is the only reason I upgraded, and only after 8.1 was released.
The root problem with Windows 8 UI was that it was clearly not designed with the intention of being a better desktop UI. It was designed with the intention of forcing users to get used to the Windows Phone-style UI on their desktop computer, in hopes that they will then buy Windows Phones out of familiarity. Basically desktop Windows had to "take one for the team". We can see here how much that helped WP.
Personally I remember the biggest pull to windows 8 for me being Games that ran on both 7 and 8/8.1, seemed to perform alot better on 8.1; they didn't advertise that it was a preferred OS or that it was designed for it.
I suspect it was related to streamlining by removing the oldest backward compatibility features, as the only apps that broke were those that ran on windows XP, most frequently they were games that weren't programmed with Vista+ in consideration (often because it didn't exist when originally released).
I specifically remember a bunch of games capping at about 20 FPS on Windows 7 and going 60-100fps on 8 when it was new using my nVidia Quadro SLI setup at the time, and having no luck finding anyone else report this on google (likely because so many people weren't giving 8.x a chance so they didn't notice).
I actually loved 8 and thought that 8.1's gui was a step backwards, the gui was extra easy to use and originally had me going back and forth between windows 7 and 8 when the performance difference eventually won me over completely as my default environment. I still kept 7 installed on another drive for the infrequent use of incompatible apps.
- the start menu covered the whole screen
- applications could only run full screen, even the simplest ones. You literally couldn't have 2 applications on the screen at the same time.
- it was hard to close applications
- it was very difficult to find the shutdown/reset/etc options
- the metro versions of "default" apps looked bad and were vastly inferior to the "old" versions. A lot of system settings ones had this problem, too (not relevant to the average user, but I use a VPN that is impossible to set up to work in the simple "metro" VPN app, but if you find and start the old win7 app which still exists, you can set it up correctly and you can even connect to it from the "metro" VPN app after that)
- a lot of computer games that worked on 7 didn't work on 8 (likely unrelated to metro UI but still a reason for many people not to update)
Some problems were fixed in Windows 8.1. In Windows 10, most of these things are fine (although Win10 gets hate because of its update system and because it installs unwanted apps, but it seems to have much more acceptance overall).
Windows 8 basically offered nothing to the average user except annoyance so people didn't want to update. It had a very nice improvement for developers in the form of Hyper-V, which is the only reason I upgraded, and only after 8.1 was released.
The root problem with Windows 8 UI was that it was clearly not designed with the intention of being a better desktop UI. It was designed with the intention of forcing users to get used to the Windows Phone-style UI on their desktop computer, in hopes that they will then buy Windows Phones out of familiarity. Basically desktop Windows had to "take one for the team". We can see here how much that helped WP.