It's ship by volume, more than weight. Big boxes take up room in the trucks, and usually are in the way for most of the ride. That is why the extra charge. weight has nothing to do with it.
That’s EXACTLY what I said ( in a roundabout way) that box and bumper ACTUALLY weighs maybe 8 pounds and costs as though it weighs 25 lbs. UPS and fedex maybe have fiddled with those specs a bit but it’s in the ballpark
