I'm amazed on various boating forums how the reaction is always "how possibly could that have happened." It's like car accidents and you wonder how. Why did car 1 not see car 2.
Well, people make mistakes all the time. Now, in this situation, you probably had a helmsman and a watch on boat boats so ultimately could have meant 4 people simultaneously making a major mistake. If the odds of one making the mistake is 1 in 100 then the odds of this happening become 1 in 100 million. However, if one boat only had one person on watch then it's only 1 in 1 million. If only one on each boat then it's just 1 in 10,000. Powerball odds are 1 in 292,000 and yet people win. Well, unfortunately, even in taking precautions, collisions at sea will still happen. Weather conditions, malfunctioning equipment, untrained or inattentive personnel increases the likelihood and that's what the NTSB will study.
Clearly though it took boat boats making mistakes. Both failed to avoid the accident. Why is still to be determined, but even with the best of us, there's always a risk. There is no such thing as risk free boating (or flying or driving) and it's due to our diligence there are not more accidents.