Easy to install and upgrade, sane defaults, good documentation, lack of waffleburgers of complexity, so I'm not sure why anyone wouldn't run OpenBSD in the first place. Granted I put Windows in the unusable bin and it's been there for decades now and sounds like it is getting worse, what passes for Mac OS X these days is not so good given that you have to disable some security thing to properly kill the annoying and disruptive notification system, among other annoyances still being fueded with, and I gave up on Linux after trying to support that waffleburger in production for a year or two.