I imagine that most people think Windows is easier because the majority of people grew up using Windows machines in schools, workplaces, etc. I think it could have to do with the sense of familiarity there.
The other problem I think people have with Linux is that the fact that different distros confuses them. Most average people are afraid of the command line, and really want a GUI for everything. Many of these people's first exposure to Linux could scare them away depending on the distro they happened to choose, I think.