One big reason, at least for me: Because OS X is the least secure desktop OS - http://venturebeat.com/2015/12/31/software-with-the-most-vul...

I also enjoy the openness of Android and the fact that it works on a large variety of hardware.

In all seriousness though, if this works as well as their little launch video show it working, 2016 could REALLY be the year of desktop linux. 'This year / next year is the year of desktop linux!' is a long running joke, but this could really be it.