It's a race dynamic. Can you truly imagine any one of them stopping without the others agreeing? How would they tell that the others really have stopped. I think they do believe that it's dangerous what they're doing but that they would rather be the ones to build it than let somebody else get there first because who knows what they'll do.

It's all a matter of incentives and people can easily act recklessly given the right ones. They keep going because they just can't stop.