The barrier isn't usability or functionality for most use cases. The barrier is getting it on the computer and supporting it. We don't have the retail & support infrastructure in place for it to be a practical option. If a non-technical person has Linux on their computer, it's probably because some technical relative put it there, and has made themselves the support person for it as well. You can't walk into a Best Buy and walk out with an Ubuntu laptop. The is an effort & technical knowledge barrier to it, and that's what I mean when I say it's not currently a practical option for a typical user.
