I don't really think this is true in non-charity work. Half of American hospitals are nonprofit and many of the insurance conglomerates are too, like Kaiser. The executives make plenty of money. Kaiser is a massive nonprofit shell for profitmaking entities owned by physicians or whatever, not all that dissimilar to the OpenAI shell idea. Healthcare worked out this way because it was seen as a good model to have doctors either reporting to a nonprofit or owning their own operations, not reporting to shareholders. That's just tradition though. At this point plenty of healthcare operations are just normal corporations controlled by shareholders.

Lots of non profits that collect money for "cause X" spend 95% of money for administration and 5% for cause X.