Here is a list of regulations placed on a commercial vehicle with a GVWR of 10,001 and up.
Commercial Motor VehiclesCould You be Subject to DOT Regulations and Not Know It? As you can see, there many added cost and regulations associated with a truck over 10,001 GVWR for a fleet. Many states will have added regulations on top of these. So there is a reason why a manufacturer would want to keep its GVWR below 10k even though the trucks other ratings are well above that. The manufacturers would lose a lot of fleet customers if they no longer offered a 10k GVWR truck. That is why Ford offers to de-rate an F350 and Ram makes their 2500 more capable.