align layers of fibers in different directions and you can get strength in different directions. But it is tricky! The glue holding the metal end caps to the carbon tube is also a possible failure point. Imagine a metal ring slid over a carbon tube held on with glue. If pressure deforms the metal differently than the carbon, you get a gap at the interface and BOOM

or if sea water degrades the glue, or if the carbon fiber degrades after each trip and eventually isn't strong enough any more, etc.