Normal people buy computers at a retail store and use it in the factory configuration indefinitely. They think about changing their OS in the same way you think about changing the type of hem stitching on your slacks.
The world is a big place and while Linux is very visible to many of us it is irrelevant to the mindshare of the vast majority of the world. Not because of ignorance, but because it legitimately isn't that important to their life.
I don't care about the hem on my pants. My pants either work, or I get a new pair. This is most people's relationship with their computer.