I can understand why the box would do that.
All to many of them are bolted down to the bed with small 1/4" bolts with only washers and nuts below the bed top rail.
Tears out in a hurry when the truck stops fast. Especially with a few tow chains, sledgehammer, hand tools, jack, etc..... Say 300+ pounds all holding on to 4 little 1/4" thru bolts.
Not too smart or forward thinking. :Oo