Earlier quoted context omitted.
Carbon fiber seems like a weird choice for this application anyway because its big advantage is in its tensile strength compared to its weight. Here, it’s in compression, not tension. And its light weight doesn’t matter.
Carbon fiber is a lot easier to work with than metal in this case because welding metal creates failure points. I don't think they could afford building a titanium pressure vessel. Weight is a factor too, carbon fiber is lighter so you can make the pressure vessel thicker and still have enough buoyancy to reach the surface(probably a good thing). From their perspective it kinda made sense even though its not safe at…
If they could they probably still wouldn't have done so. The founder who was onboard the Titan was known for calling safety regulations unnecessary and a barrier to "innovation", like a window only rated for a depth of 1300m used at 4000m.