The ship doesn't need to withstand the wave without any damage - that would be unnecessarily expensive. But they should at least be designed to withstand such a wave without sinking.
If I climb on a ship and you tell me "well, there's a 1 in 100'000 chance that we'll be hit by a freak wave and then it's quite likely that everyone on board will die, since the ship will be broken in half and sink", that's a very different thing to say than "well, there's a 1 in 100'000 chance that we'll be hit by a freak wave, and then the ship will sustain severe damage but should be able to limp back to shore or at least float long enough for a rescue."
The difference between those two scenarios is probably less expensive than you think.
The solution probably isn't better ships, but better mapping of wave conditions and routing around more dangerous areas.