Implosions require a lot of pressure, so whatever took them out did it while they were still deep.
My guess is it happened as they approached extreme depths. Metal fatigue and poor design aren’t always instantly apparent, but they stack up exponentially. The same way the CEO had piloted it down before he did again, then BANG and done. Would have been practically instant and without warning.
Worth pointing out that only the end caps were metal (and titanium at that, which is already brittle), while the bulk of the hull was carbon fiber, which doesn’t gradually fatigue, it fails catastrophically.
Also, they lost signal at 1 hour and 45 minutes into a ~2 hour dive. I don’t know how much their dive rate varied, but if we assume it was effectively constant, that puts them at ~3500 meters at LOS.
Combining those two points, two to three years after building the ship, they identified cyclic fatigue in the carbon fiber that reduced their calculated rating to 3000 meters. Since that’s not enough to get to Titanic, they completely rebuilt the ship, two years ago.
So yeah, I think you’re right. With the public facts available, I think the most likely scenario is the carbon fiber hull was fatiguing again, they decided to trust their acoustic/strain monitoring system that they believed would give them enough warning to resurface (which the guy they fired in 2018 said might only give them warnings milliseconds before there was a problem), and it failed somewhere below 3000 meters.
