I can think of one reason: Steve Ballmer
Last night I saw a commercial where they actually had to explain how to use Win8. I knew then, it was over.
How bad do you have it?
Five reasons why Windows 8 has failed
Because, from the end user's POV, it breaks everything they've become used to for the past 18 years (since Win95).
2 hints, for anyone stuck with Win8 on a new PC or Laptop:
1.)Classic Shell is free, and will give you your start menu back.
2.) "Downgrading" from Windows 8 to 7: What you need to know
Obligatory Linux plug here.