I think sometimes we abstract society too much. As always, remember that society is just large numbers of individuals. So why might you decide you want to help people in this sort of situation? It's reasonable to speculate that Musk may have had some of the following major motivators, for instance:
1) It's a fun challenge to try to solve, particularly when traditional solutions seem to be failing.
2) You get to help some people.
3) It's great publicity for you and your companies, particularly if you succeed in an out of the box way.
And other people would have of course have had radically different motivations for why they chose to get involved. There's no grand overseer that found it reasonable to 'spend' or risk a life. It all comes down to completely subjective views, motivations, and value systems. So if you want to know why what any given individual would do is something they would consider reasonable, you would need to ask them. There is no right or wrong answer. In this case the diver's motivations and value determinations convinced him that this was a reasonable spot to risk his life, and he died. I expect he had no regrets and so it was, all things considered, a great way to die from his perspective. By contrast, it would be a terrible way to die from the perspective of many others. Nobody's right, or wrong. It's just different motivations and value determinations.