I absolutely could not believe how drastically different, lurchy and horrible Windows 8 is. I'm just a basic computer user, do not need anything advanced.
I've never had a platform, program, application (or whatever the fuck everything is called) infuriate me as often as 8.
What was the logic behind making such a drastic change to such an easy fucking system?
Cost.
Windows 8 was a new kernel, designed from the ground up to be run on multiple platforms with code being shared across completely different hardware.
Windows 8 can run on an ARM-based phone, an ARM or x86 based tablet, a laptop, a desktop, or a massive server.
This saves Microsoft hundreds of millions of dollars in not only R&D but support. Because they are reusing 80% of the code of the operating system.
The problem is that they assumed desktop users wouldn't care, and that server users basically wouldn't have a choice.
So they focused on mobiles and tablets and basically backported the experience to desktops and servers. It was a monumental mistake, and it's what caused all the shake ups that happened at Microsoft since.
It's not as widely talked about, but Windows 8 is a bigger flop than Windows Vista. The only difference is that Windows 7 is a better operating system in all respects to 8, which wasn't the case for XP vs Vista (Vista was still better, just glitchy/buggy).
Windows 10 really needs to be good, or they'll lose their final group of power users and developers (like me) to Mac OS X.