The cynic's answer is that human health is something that really rich do not have much control over. (SJ is just one shining example)

In other words you get billion dollars but realize it is all for naught as you will be worm food in 100 years.

So some go full Kurzweill, some find/found religion, some do a bit of everything.

This problem is not unique to billionaires but they can attempt to roll a bigger rock up the mountain.