Sailandoar makes some very good points, and ones that I'd strongly agree with. Many deep draft boats are less than seaworthy, and having a shallow draft doesn't automatically make a boat unseaworthy. Especially in the case of multihulls. Many catamarans have made long bluewater ocean passages, and were designed to do so. The Gemini Cat has an EU RCD rating of A, Ocean.
Many more hurricane holes are open to a boat with a draft of less than 3', than are available to those with drafts of 5'+. And fewer boats are competing for those same hurricane holes just before a big storm hits.
Many more marinas are available to boats with shallow drafts, as well as many more protected anchorages. Having more choices means keeping the boat in a marina slip might be less expensive—more choices means a wider price range.
I sail a trimaran, and it only draws 18" when I have the board up. It is designed, like many of the cats, to be beachable, and doesn't mind sitting on the mud or sand when the water dries up.
Some people will say that multihulls have the disadvantage of turning turtle—capsizing and not re-righting themselves. True.
However, a properly sailed catamaran or trimaran is very difficutl to capsize, primarily due to the great inital stability their form provides. Most non-sailing vessels can not re-right themselves, including most large merchant ships, fishing trawlers, military ships, etc.
Many monohulls have the problem of sinking, as they fill up with water and can not recover, once they have been knocked down.
They will re-right themselves, and be very happy, sitting on the bottom of the ocean, right side up. However, a multihull has a far higher chance of not sinking, as most are made of buoyant materials, and have no heavy cast iron or lead keel to bring them to the bottom.
Multihull designs go back thousands of years, and were used by Polynesian islanders to make ocean crossings in the southern Pacific, long before the monohulls used in Europe ever did.
Catamarans provide a great deal more living space than a comparable length monohull. The smaller catamarans are more weight sensitive than their larger counterparts or comparable length monohulls, due to their low mass and relatively narrow hulls. However, if you can resist the urge to load up a sailing cat with everything in the world, you can sail them well and far faster than a comparable length monohull.
One of my favorite videos making this point is located on this website
Trimarans, while generally providing better sailing performance than a catamaran, will also generally provide less space than a comparable length monohull, at least in the smaller sizes. In the very large sizes, the amas and a bridge deck can make the trimarans very spacious, but these are both very rare and extremely expensive. I regularly outsail 40-45' boats on my tri, and my trimaran is not a lightweight, outfitted for racing and camping on water type trimaran.