I have spoken to LOTS of different people about published tow ratings.
One answer that sticks in my head is "Vehicles are crash tested with certain equipment installed".
So, if a van has a 3600lb hitch installed, and it is tested for that, then that is what is published. Even if the vehicle is able to tow much more safely.
For example a Subaru Imprezza has no tow rating published an North America, but is rated for 1500lbs in Asia and Europe. The Subaru XV Crosstrek, which has the same engine, transmission, drive train AND unibody construction IS rated for 1500lbs. So, most mini-vans are rated by the original crash testing done back in 1984 on the original Caravan. With better engines, drivetrains and body construction, add traction control, brake control, etc, a larger trailer should be able to be towed safely.
2012 Dodge Grand Caravan with Prodigy P2 Brake Controller and AirLift air-bags
2004 Jayco Eagle 14SO Pop-Up