Why? Because they are cheap. I bought a 7000lb rated car trailer a few years back and discovered days later the coupler was a 5000 lb rated one. Called the manufacturer who said "Oh it will be fine don't worry" I asked them to put that in writing so if it ever broke and caused an injury or death I'd have proof they said that.
They declined but sent a guy to town who cut off all the couplers at the dealer and mine and welded 7000 lb rated couplers on
