The memes write themselves, ladies and gentlemen.
The problem is the use of CF and titanium. Traditionally you’d machine a big block of titanium into a hollow sphere for sub’s pressure chamber to withstand that much pressure. The Titan is different in that it’s a cylinder with hemisphere plugs. While many submarines have used this shape these other submarines also a) doesn’t dive anywhere nearly as deep and b) aren’t using 2 different materials (titanium caps and CF cylindrical body).
Other deep dive subs use a spherical pressure vessel because it is the most efficient use of material to withstand the pressure at the sea floor. The trade off is that you have a lot less internal volume. While you can probably design something by with a tube and cap shape to withstand that load, the joint between the cap and the tube needs to be carefully design and built, and will likely need to be reinforced to withstand the same pressure. Doing this all out of titanium is probably prohibitively expensive for a startup company, you can probably machine a shape like that without a joint as well but that’s likely to be even more prohibitively expensive than trying to join them.
The titan tried to cut that cost by using CF composites for the tube section instead but I have serious reservations about how it’s used here. This is because the primary load from water pressure on a sub is compression, carbon fiber’s primary strength is in tension. So you need to build the structure in a way that translate the huge compression load into tension to best take advantage of the CF. If you don’t then it’s a waste of material and you probably could build the sub more efficiently (mechanics of material wise) with a different material. As expensive as CF is, it’s probably whole heck of a lot cheaper to build the cylindrical section out of CF than Titanium. Of course they pay that price with a dubious ability to meet their requirements of surviving multiple trips to a depth of 4km.