Reasons were the excellent jails system, the ports collection, the ZFS on root (though Ubuntu is starting to offer that) and the great documentation. I also don't like the scale of corporate involvement in Linux development. In the end that leads to companies trying to insert their own IP with a view to monetisation (like Ubuntu with Mir, Upstart, now snaps). It's also the most suitable for a desktop system of all the BSDs I think.
But it's not for everyone. For one the hardware support is limited. I didn't even bother trying to get the WiFi or bluetooth going (I run this on a pure desktop). For laptop use I'd use a flavour of Linux, though I'm not entirely sure which I'd use :) It also doesn't hold your hand as much as most Linux distros, though it's not nearly as barebones as arch either! I'd consider it something a bit in the middle like Manjaro. Overall I'm really happy with it though.
I still use Macs for work though and I administered them for a long time. It's always a struggle if you need to do something that Apple doesn't really want you to do. You may get it working, but there's a good chance it'll get broken in whatever minor patch that's coming along without warning :) Unfortunately in a business with less than 1% Macs you can't always do things the Apple way.