On dives you would hear cracking noises. The noises would become more severe as the vessel dived deeper. The hull may have been replaced one or more times over the years.
What makes cracking noises? Cracking of course.
So with each dive Titan's hull would become increasingly fatigued (i.e. cracked), and thus weaker.
The recovery of hull fragments may provide evidence to support the theory that the carbon fiber hull finally failed.