SIncere condolences to the family
Having gone through the experience of drowning (actually near-drowning technically speaking as I'm still here), I can understand a victim may not have be able to think straight even when confronted with what some may call a "simple" problem, once the process starts. Simple "logic" such as dropping a weight belt is not at the forefront of one's mind. Lots of basic instinct reflexes take over, panic is hard to avoid. The focus is easily drawn to trying to figure out where the source of the problem is (e.g. a failing reg to use a hypothetical example), rather than to think about where the back-up solution is. Even trained and experienced divers may behave in unpredictable ways. There is not much time to address the situation correctly.
I compared it to being involved in a car accident. You MAY be able to respond correctly if you are quick, but sometimes the situation may take over and you will respond instinctively, not necessarily adequately to correct the situation. Of course you are more likely to respond correctly if you had regular and repeated exposure to the same problem.
Reality of life is that diver training does not include further regular monthly repeat drills and practicing of skills to make us more self-sufficient in case of emergencies. Many of us get trained once or twice, some of us will take regular refresher courses, few of us are really trained in the "drown-proofing" repetitive way navy seals may experience, until the correct response becomes a true reflex action. I'm certainly not.
Of course we don't know 100% what happened, we just need to all be aware that it may be that nobody is to blame.
A lot of scenarios can be practiced and reflexes can be fine-tuned, but you can only expose a diver up to a certain level of experiences. When real **** happens, we may all still respond in ways we never imagine.