In Ubuntu, the mouse pointer disappears after locking the screen or suspending [1], and the Fn button combo can take minutes to change screen brightness [2]. These bugs have been around for months and years, respectively. You simply cannot get non-power users to use an operating system with issues like this. Perhaps there's a more polished distro, but if the one that's touted as the beginner-friendly one has such obvious user-facing problems, it's just not feasible to get past 1% market share.
[1] https://bugs.launchpad.net/ubuntu/+bug/1573454 [2] https://bugs.launchpad.net/ubuntu/+source/gnome-power-manage...