One of my family members was a research director at the UN and came from a middle class American family. It has its problems (he certainly has his share of complaints) but the idea that they are all nepo babies is incorrect and they do have serious researchers. Also, are we sure that the $10.5 trillion is a UN generated number? Other people in the comments seem to think it was made up by some other organization.
A relative of mine worked for the UN and interfaced with the UN after they left for a non-profit. Anyone that knows anything about them and also just simply observing what and how they are doing things should have no doubt that it is filled with people that got there by using their connections. And you absolutely constantly run into people that have no business being there other than through nepotism. Btw. I am sure that US staff is less likely to be a total nepo baby, but because the UN "has" to hire from all over the world, most roles are not filled like that.