GVWR and GAWR

Could someone please tell me why GVWR is less than the manufacturer specification limits for GAWR front plus GAWR rear?

Only the vehicle manufacturer can tell you why they chose the trucks GVWR or FAWR/RAWR.

In fact some of the new model trucks have GVWRs close to the sum of the vehicles axle/tire load ratings.

The trucks GVWR isn't used in a legal sense as how much load any truck can carry. Thats determined by the vehicles axle/tire load ratings.

Most TCs on crew cab trucks add little to no weight on the trucks front axle so watch those 6084 RAWR numbers.

Every truck owner should know his trucks front and rear unladin axle weight numbers.

Example; I've seen lots of 2500 4x4 GM owners have around 2700-3000 lbs unladin rear axle weight which leaves them around 3000-3300 lbs of payload. Get'r weighed.
Now don't stress out here as the only difference in your 2500 GM and the 3500 SRW is the SRW has higher rated rear spring pack/wheels and tires. GM uses the same big 11.5" AAM on the 2500 and 3500 DRW/SRW trucks so you sure won't stress the axle.

A google on your question has lots of opinions on the GAWRs = GVWR.