Home stuff was the last holdout for me, but even that has been replaced by Proxmox these days. I used SmartOS for a solid 7-8 years, though, and like it for most of that time.

I couldn't point to any one single major reason that prompted the switch - just lots of small annoyances stemming from the world expecting you to be running Linux instead of Solaris, and once you move away from zones, you lose one of the most compelling reasons for being on SmartOS