car haulers
I have seen very few car haulers with the gooseneck. The only ones I have seen were for semis, and they had lots of undercarriage support. Anyhow, the reason that a fifth wheel should be used, is due to the trailers' flexibility (less trailer weight so more payload) and the added flexibility from mounting on a gooseneck ball. A fifth wheel hitch is more stable and has a better locking power upon the kingpin.
Hideabed Inc will only use fifth wheel hitches on their trailers, except for one small exception. They will use a gooseneck hitch to pull the trailers off of the assembly line and out into the yard. When customers inquire, they flat out admit that their trailers are too flexible for a gooseneck and will pop them off of the ball. They actually show inquisitive customers what happens. They hook onto a trailer, drive it into the parking lot, and will pop them off right there in the lot for the customers to see. I had the pleasure of talking to a long-time engineer, and now salesman, and he informed me to these facts, and to other car hauler designs. Goosenecks are designed to carry a lot of weight upon the ball, and car haulers just don't do that. They stay light and flexible, except for the designs that have a lower floor frame level with the axle centerline or are fully supported from there up to an angled ramp.
That car hauler in the pic sat way high, and looked light. It also looked like the owner used a gooseneck adapter instead of an original equipment fifth wheel hitch. It wrecked right at an intersection, and I suspect he hooked a tire onto a curb, flexed the trailer off of the ball, and dumped it all right there.
Sorry for the long post.