The straightforwardness appealed to me, it's a binary distribution with a rolling release cycle and no custom-finagled packages.
But after a while, I got tired of manually configuring everything, doing all kinds of weird house-keeping and having to randomly boot from a USB stick to rescue my system from some update with untested consequences. And this was while running the supposedly "stable" update branch. I also got tired of the countless updates that required manual convoluted update procedures and Pacman tricks to function correctly.
Maybe this was because my install was relatively old, and thus had stuff like Pulseaudio and Systemd grafted on top of it, but I never had any issues immediately after those updates.
So around a year ago when Linux Mint 18 was released, I made the switch and I haven't looked back. I know it's a hackneyed phrase, but Everything. Just. Works. I have not had to do anything at all on my refurbed T420, I just installed it, and it just works, it's wonderful.
I cannot be arsed to mess around with configuration files and whatnot on my computers anymore, I have much more interesting things to do than mess around trying to keep my personal computer running correctly.
I was also a hardcore KDE-head for years, but Cinnamon has really grown on me. It does what I need, the way I want it (I grew up on Win9x, so that's the interface style I prefer), without getting bogged down in obscure configurations or arcane frameworks.
Maybe this all marks me as fallen from the ranks of the Linux cognoscenti, but I don't care. I just want to get on with my life. In the same way that I see a lot of people gush about Mac OS, Mint simply gets out of my way and lets me get on with stuff I actually want/need to do.