Mostly ease of use. It's a rock. I have a special place in my heart for BSD, but that aside, when the SystemD battles started and I was on Ubuntu, I was interested in using ZFS for a few things. So the choices were ZFS on Linux, or go back to BSD. After about an hour of playing around, I ended up back on FreeBSD.
So, it's partly personal, as all things are. But it's mostly how easy it is to use, especially for someone that wouldn't describe themselves as a server admin of any special level of skill. There are a few core tenets of design in BSD/FreeBSD that are both beautiful and very easy to understand. So I can ignore the OS a lot of the time and just get to work on the app side.
