because, you give in to the hype too much
Vista wasnt a complete flop. It was a huge stepping stone to what 7 achieved. No release is ever a massive failure cause what problems arose from the release ultimately helps the next version.
Vista was a big milestone leading up to 7, namely aero and compositing, unified device drivers and a better file manager. All of them are in 7.
I don't know why people are baggin on vista. If you take a look at linux (specifically gnome) there are MORE bugs in it every release (6 months) and more patches to download than windows.