Air pressure decreases as you go up at a far lower rate than water pressure increases as you go down. Air pressure at 30K feet is ~0.3 Bar compared to 1.0 Bar at sea level.

Water pressure increases by 1 Bar every 32ft (10m) of depth. To see the equivalent change in pressure in water (0.6 bar) as you see going up to 30K in the air, you only have to go down ~20ft (6m). The pressure on the submersible at 9000ft (2750m) is 276 Bar.

F16s and other planes with composite body panels will sometimes lose a panel due to water buildup between layers of the composite. The water freezes between the layers popping the panel loose from the frame or retainers holding it in place. That is usually not a life-threatening problem (though not desirable). A crack in a submersible pressure vessel at more than a couple hundred feet is usually fatal.

The description of the Byford Dolphin accident in ~300ft (~90m) of water or 9 Bar pressure, is illustrative: https://www.iflscience.com/byford-dolphin-accident-how-livin...

The pressure on the Titan would have been ~30 times greater than what occurred on the Dolphin.