It may have something to do with the semi trucks that pull those types of trailers, the nickname is "Wiggle Waggles". The trailers that I've noticed with wheels at all four corners seem to move around an inordinate amount. Not anything I would care to tow behind me.
However backing one would be an easily fixed issue. You could have a mechanism that locked the hitch so it wouldn't pivot at the ball when backing up. Then you only have one pivot point.
If you're seriously overloaded a better solution might be one of those add-on 5th wheel hitches that mount behind the truck.
