That is indeed the case, a catmaran would be hard to accommodate or maneuver in existing docking facilities. I've never seen really large catmaran designs seriously proposed by any real naval architects (although they are very common in "Popular Mechanics"-type venues). Perhaps there is some structural reason why this design won't scale up, or maybe it would just be too expensive to build. I do know that in small craft, where multihulls are a popular concept because of their many advantages, they are often considered too light for most applications compared to monohulls.

I think the major factor is fluid mechanics. A displacement hull's top speed through water is constrained by its overall length. The longer it is, the faster it can go, and there is always some limiting hull speed determined by hull length, regardless of how streamlined or slick the hull is. Hull speed is related to fuel consumption. Unless you abandon the displacement hull altogether (as in hydrofoils or planing hulls) it simply becomes too energy-expensive to push a really big catmaran, two hulls might be more stable, but they would consume too much fuel for a given length, you can go faster and burn less fuel with a longer single hull.

In sailing craft, cats and trimarans are planing designs and extremely fast, and they have high initial stability, but they cannot carry as much weight as a displacement monohull, and of course, they have no final stabilty. Once capsized, they tend to stay that way. They also are forced to be very lightly built, in order to be able to get up on a plane. In rough weather, they must be handled very differently than a traditional monohull.