Orma 60 was actually an open development class - cats were class legal and at least one was built.

The tri is a unique solution here because the DoG limits the boat based on Load Waterline Length. With the tri, you can mostly float everything on the center hull which nails the load waterline limit. Meanwhile, the amas barely touch the water at their deepest rocker...hence why we see the huge bow and stern overhangs on the amas on DogZilla. Since the center hull should ideally be flying, it's water shape is less important than it's measurement shape. It also allows for the weight of the boat to change significantly without affecting the measured LWL...for instance...changing different rigs and adding crazy things like rigid wings.

The catamaran has a tougher time pulling this off and the loading/weight has to be precise to get the measured LWL right - presuming they're trying to get the same kind of overhangs with the benefit of an extended hull length under sail. Getting LWL and weight right also dictates the hull shape more-so than the tri. The tri's ama rocker / shape can be optimized for sailing without much regard for static measurement since the center hull carries the burden for that.