Its not necessarily an implosion that can kick off a cascade of failures, a thruster could have gotten stuck and sent them into a spin. It looks like the submersible was heavily dependent on software if you take a look at a few the videos explaining its construction.

All those switches covering the walls of the Alvin sub (or any other real scientific submersible for that matter) are there to control every aspect of the sub at a hardware level. It doesn't look like the Titan had that level of control, at least not accessible quickly in an emergency.