Because most users, don't want to leave their comfort zone. They are afraid to change, as windows was here earlier than Linux. In my experience you can not convince users to change their working environment to Linux or Open source over night you got to make their transformation by phase or step-by-step. Say, first make them use and familiarize in using Open office instead of MS Office, coz this is a software that most ordinary users use. Then you can make them transform gradually to Linux, be it Mandriva 2007, Ubuntu 7.04, Fedora 6 or any Linux distro u want them to use. I still remember in our LAMP group (Linux, Apache, mySQL, PHP/Perl) that one of our strategy to make Linux more popular is to make Internet Cafe use Linux, this the place where most ordinary users go and use computers.
When it comes to support, I don't recall back in time that MS people go to my place and fix my OS. When it comes to documentation, well have you ever downloaded an MS Reference manual online for free?? In open source a lot of opensource manuals are downlable for free. And when t comes to bug fixing, I don't have to wait for the next patch release just to fix the bugs. Just post your issue and in several days a bug fix can be already download, that what Open source is all about, a lot of eyes is on the source code. You see guys, I don't hate Microsoft Windows, it's just I don't like it!
Quote: To Avoid the Gates of Darkeness, use LAMP.