Limiting factor on GVWR for trailer

Wondering what is creating the limit of 5500# and why they didn't give this trailer a 6000# GVWR which seems to me would still keep it under the axle and tire limits.

The feds allow the vehicle maker to determine any GVWR or the GAWR he chooses. There is no single formula how all the mfg will make those determinations that I've heard of.

We do know 49 CFR FMVSS fed safety regs that the mfg is required to follow says; This paste and copy is a part of 571.110 regs; 571.110
(snipped)
S9. Each motor home and recreation vehicle (RV) trailer must meet the applicable requirements in S9.

S9.1 On motor homes, the sum of the gross axle weight ratings (GAWR) of all axles on the vehicle must not be less than the gross vehicle weight rating (GVWR).

S9.2 On RV trailers, the sum of the GAWRs of all axles on the vehicle plus the vehicle manufacturer's recommended tongue weight must not be less than the GVWR. If tongue weight is specified as a range, the minimum value must be used.

S9.3 Each motor home and RV trailer single stage or final stage manufacturer must affix either a motor home occupant and cargo carrying capacity (OCCC) label (Figure 3) or a RV trailer cargo carrying capacity (CCC) label (Figure 4) to its vehicles that meets the following criteria: (snipped)
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Now when I purchase a flatdeck or a equipment traileor a car hauler the sum of the axles ratings is usually its GVWR. My last GN trailer was a tri axle with 6k axles and it has a 18k GVWR. The trailer can carry up to 18k on the axles. The truck carries the hitch/pin load.