The truck maker may choose any GVWR or FAWR/RAWR they want for a particular truck. No one knows why or how they make that determination. There are some things we do know....
One thing we do know is the trucks GVWR cannot exceed the sum of the truck makers FAWR and RAWR.
We also know the truck is fully capable of operating at the sum of the GAWRs as evident every commercial truck out here carries weight above the trucks door tag GVWR.
IMO registration has little to do with it as some states like mine have no weight registration requirement for a private use trucks. We simply carry weight up tor the trucks makers GAWR/tire load capacities for each particular truck.
Use the GVWR or RAWR for load carrying math. Both are safe.