That, and it had a lot of technical changes that broke a lot of drivers and programs. All the technical changes also had lots of bugs that needed to be fixed. And also, Microsoft OK’ed Vista for 512 MB RAM when it should have had at least 1 GB.
When everything started to smooth out, bugs fixed, drivers and programs updated, and computers came with 2GB+ RAM, then Microsoft released Windows 7, based on all of this, and that made Windows 7 shine.
People say that Windows Vista should never had been made but without it, Windows 7 would have suffered the same fate as Vista.