Does someone always have to be at fault ?...
No, someone does not always have to be at fault. Having said that, there are some design and build issues with these ships.
When Bayesian sank, my first thought, for some reason was, did she had a movable keel? I had never heard of a ship having such a keel so I figured that could not be an issue. Then I found out the ship did have a movable keel and it was raised when the ship sunk. So, one question led to another and I started to really pay attention to the situation. The best information has been on The Yacht Report YouTube channel which covers these ships.
There are some design and build issues that raise questions some of which we already know the answers. The raised keel is not likely to have been the reason the ship sank. The AVS was low with the keel deployed, and lower when raised, but the AVS was still higher than the down flooding angle which is 40-45 degrees. The down flooding angle is gong to be the most likely initial source of flooding of the ship. Witness statements seem to indicate that ship heeled over past the AVS even if the keel had been deployed. The low AVS of the ship is certainly going to be questioned.
The port side hatch was closed based on photos taken by guests/crew returning to the Sir Robert Baden Powell the evening before Bayesian sank. I think it was the previous Captain of Bayesian who said this hatch was always closed unless guests/crew were getting on/off the ship since the hatch was closer to the water due to more ballast to handle the taller mask than other ships in the class. One would expect that hatch to be closed when not in use, and especially at night, if for no other reason than security. If that hatch is found to be open it will be a surprise. Flip side is the hatch is on the port side and the ship sank on it's starboard side.
The builder CEO has gone on and on about this hatch but all the available evidence says the hatch was shut.
Crew has reported that on other ships in this class, the glass doors to the interior would open when the ship was heeled over and have to be tied shut. There is at least one video of the crew trying to secure this opening.
The aft cockpit is a below the deck with steps port and starboard. This would seem to allow water to be scooped up into the cockpit. The cockpit has the glass doors that open when the boat is heeled. The investigation will say if this was a problem or not. There is also a forward cockpit with doors that are offset to port and starboard. If the starboard door was open when the ship heeled it could have caused down flooding. But if the ship was blown over past her AVS this might be a moot point.
The crew and/or guests reported that when the ship heeled over the first time, she appear to go over at least twice, furniture and locker contents went all over the place hindering movement. The divers recovering the bodies where hampered by debris including wiring which I thought was odd. This may have hampered the guests down below from escaping.
With what is currently known, the AVS and the down flooding are the most likely reason(s) the ship sank. The other issues may have been links in the chain of events of the sinking, or just made things worse, but we won't know until the investigation is complete.
If the low AVS and/or low down flooding angle caused the ship to sink, who is to blame? The designer? The owner for approving the design? Was the boat built differently than designed and the builder is at fault? Or is it just a chain of events that led to a sinking and nobody is really at fault?