You will find low carrying capacities particularly on "ultralight" towables. The designers shave parts sizes everywhere to keep weight down, frame and suspension is part of that. Also in that market, there is a tendency for the buyer to look at GVWR as the towing weight, thus GVWR has to be kept down to sell a trailer as lightweight.
Motorized RVs end up with low CCC simply because the manufacturer is building too big of an RV for the chassis. C's are kind of stuck with their 14,000-14,500 chassis, but even going up to 16,000-19,500 in a Super C, they would again build too big a house, sometimes to within 1000 pounds or less of chassis capacity. It happens again when they try to put 38 feet of house on a 26,000 diesel pusher chassis, rather than going up to the 33,000 chassis.