The news says: "In almost all of these things, there's not one thing that happens; it's a series of things,"
I think it's just hard to predict. This probably doesn't happen often enough to know what expense is justified in preventing it. They already had many safety measures, so if all of them failed, one extra gadget could just as well fail too. Then what? Put two cut-off valves on the pipe? 10? Give up drilling altogether?
And what happens when the cut-off valve accidentally fires? And it also breaks the pipe because it's a bit rusty after all that time, so you get an oil leak where normally there wouldn't be one.
Every disaster could be prevented, but to do that would mean grinding the economy to a halt. It reminds me of 9/11. Suddenly everyone had the idea to install evacuation slides or other gadgets for people to escape by the outside of burning buildings. Or nuclear power where the safety guys won, and now nuclear is safer than coal - but at the expense of the economy, and now the environment too.
