I've used all flavors of Linux (from Gentoo, when there was no installer and I had to use dd, to Ubuntu). I still love Linux, but I don't use it anymore as my main system. I have 2 problems with it:
(1) I want the computer to work for me, not the other way. I used to like to hack everything on my computer, but after years and years of doing that, I've lost my patience. I want things to just work and not break after every damn update. I want to be able to do my real job and use the computer as just a tool.
(2) It looks ugly, the fonts are really bad, nobody cares about UX when designing apps, etc. You can say that I can change that, but as I've said: I want the damn thing to just work out of the box. I understand that maybe you don't care about that, but that's why it's me who's using a Mac. Don't get me wrong, it's nothing wrong in using Linux, it's just not for me anymore.
I'm still using the command line more than the GUI, though. But that is a choice. It combines the best parts of both worlds.