I was brought up short by that "over 200 in two decades" figure, too.
Roughly one supertanker or container ship gone missing, without a trace, every month.
I'd be more likely to blame piracy than "monster waves".
Wonder if any of these sinkings have ever been caught by surveillance satellites....
Another odd thing is that I've read quite a lot about large waves and I've NEVER heard them termed "Monster Waves"....they are universally called ROGUE waves.
Arr, ye scurvy cur! I had nothin' t' do with that! I was diggin' up me trreasurre!!