Though it pains me to admit it. Most modern cats have at least 6 appendages waiting to be struck. Furthermore, they are mostly delicate. Small rudders, saildrive, daggerboards, sacrificial minikeels are all easily damaged. Most monohulls have either a full keel with attached (and therefore pretty well protected) rudders or a large fin and a rudder generally bigger in size and heft than a multihull's rudder. Even a modern Open 60 with a long, deep, pivoting keel and narrow chord length is by definition heaviers and requires greater engineering than our small, light weight appendages. We have greater odds of a strike on one or more appendages and we sweep a larger swath of sea where obstructions are laying in wait. While it's true that modern monohulls also frequently have saildrives or props that can get damaged, they tend to be well hidden behind a rather substantial and deep keel which does a better job of deflecting flotsam also.