An interesting question and discussion on Reddit.
My humble opinion: Linux users don’t know about it. And also, the undeniable “fashion” of going with whatever is hot at the moment.
As more Windows people try Linux in recent years the very first they see -or get recommended- are the well known ones like Mint, Ubuntu, etc. The recent influx of eye candy alternatives like Omarchy or Hyprland doesn’t help either.
Mind you, I was a happy XFCE user for many years, tried KDE, i3wm, bspwm and Hyprland. Openbox was a mere curiosity here and there… and then, several years ago, a new release of Mabox accidentally caught my eye in Distrowatch and here I am, even happier and feeling at home every time I turn on my computer or visit the forum.
I wouldn’t change a thing about the most important parts of Mabox:
- Manjaro is well established and stable. The likes of Arch throw updates every single day and even if they don’t break it becomes tiresome.
- Openbox sits in the very frontier between Windows Managers and full fledged Desktop Environments, meaning it’s light, versatile and fast.
- No one (and this is not a cheap praise), no one else, put this amount of effort and care in order to make Openbox and Tint2 friendly, beautiful, approachable and customizable as you did. The good fellas in our community also deserve a huge hat off.
Current improvements and future editions based on Labwc and Noctalia will make Mabox even better. You did, and still do, a magnificent job; don’t doubt it for a single second. 
Kind regards.