Tubs

One reason tubs are preferred over clinchers for cyclocross is that the low pressures you run often aren't enough to hold a clincher on the rim. Remember that tubs use glue to stay on the rim, clinchers use the pressure in the tyre.

I have a clincher fat bike wheel in my workroom running 9 PSI. No amount of bashing about has caused the bead to move. So I'll be using it at that pressure.

The reasonings are lighter rims, and reduced pinch flats.