In this case, the "test flight" had already been taken - this was not the first dive to the Titanic by this specific sub. So, the real risk may be in the number of dives needed to fatigue the carbon fibre structural material to the point of failure. That is hard to determine without testing a bunch of such structures to actual failure - a very expensive process. I read that this sub had experienced 24 previous pressure cycles as tests and dives. But, that doesn't really tell us that an identical one couldn't fail at 20, or couldn't last for 30. And, an "improved" design may be far better - or unexpectedly worse.
There is always going to be some risk in going into space, or deep under the sea, or climbing Mt. Everest, or even hiking the tourist trails in the Grand Canyon. It would be a shame if there was a bureaucracy that could tell individuals how much risk they can take when they want to do something adventurous. But, there is always a reaction to a loss of life to try to make sure that "it never happens again", especially if there is a bureaucracy that is given the "responsibility" to make sure that it never happens again. So, there is a tendency for over-reach built into bureaucracies.
On the other hand, when these things go wrong, it often pulls in government resources to respond, and that can cost more than money. Sometimes, responders are put in great danger to save the lives of stupid people. So, there are some laws and regulations that limit what a person can do on the basis of how dangerous it is to themselves, even if not to others. Often, for instance, trails are closed due to avalanche danger, animal behaviors, etc.
But, it is a difficult decision to determine where the government should be allowed to regulate individual risk taking.