The GVWR is the maximum allowable total weight of the loaded trailer.
For regulation compliance of trailers, the Cross Combined Weight rating is more often used along with the individual axle weights.
That is;
a) The weight that each axle is putting on the roadway. There is a legal maximum related to tire size and number.
b) The total weight of the truck and trailer(s). There is also a total legal maximum which is often less than the sum of the allowable axle weights.

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Ohm's law
Not just a good idea;
It's the LAW!

So the GVWR does not have to do with the structural capabilities of the frame itself? Just simply the axle weight and weight of trailer itself?

presumably the trailer is sized to the required weight ...

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

The load carrying capacity of the trailer will be the minimum of the structural capacity of the frame, the structural capacity of the axle, the capacity of hubs, the capacity of the rims, or the capacity of the tires. the structural capacity of the frame is calculated from the section modulus of frame members and the position/pattern of the loading AKA the weight distribution.