Towing capacity vs max cargo weight rating

Why doesn't Ford just state that your RAWR number is the only number to look at (for payload purposes)? Just musing here, you don't have to answer - this stuff is confusing a bit once you start digging into it.

Not really.
In Fleet Ford spec pages showing all the weight number for the different model selections in par. #4 in all the weight pages says :
"
4) (sniped).. "Front and rear GAWRs will, in all cases, sum to a number equal to or greater than the GVWR for the particular vehicle".. (sniped).
What Ford is saying is if they wanted they could sum the axle rating for the trucks GVWR.
Now anyone can guess why they do or don't do so.

NHTSA home page several year back gives us some hints: I paste and copy these type documents as after a certain period of time (years) their no longer available .

GUIDELINES FOR CALCULATING GVWR
Manufacturer Specifies GAWR and GVWR
**Vehicle manufacturers may determine the GVWR of a vehicle by calculating the maximum load rating of the vehicles axles, tires, brakes, frame, suspension and wheels in order to come up with a GVWR rating. Also, a manufacturer may limit the GVWR if so desired. So they could have the componentry to rate higher but choose a lower rating at their discretion for excise tax purposes."**

**The sum of the GAWR’s must at least equal the specified GVWR to avoid overloading the axle systems, and the GAWR sum may, of course, exceed the GVWR. Typically the manufacturer balances the commercial advantage of specifying a higher GVWR against the expense of higher
GAWR’s”. GAWR Determination Includes Tires, Wheels, Brakes and Suspension.**

The 'commercial advantage' it mentions can be where marketing come's to play.

All said and done.... DOT doesn't use a trucks GVWR or the payload sticker for determining how much load it can legally/safely carry.

And of 'course our trucks don't have a GCWR or "tow rating" placard requirement per FMVSS 571 requirements.