What is so hard about understanding their desire? They want to keep more money for themselves so they can buy more yachts, invest in more things, whatever. This is just how humans are.
It's up to policy makers (i.e. government when it comes to taxation) to structure the system to mitigate the inherent self-interest that people have. Obviously that's easier said than done when the ultra-rich buy off the politicians, but human nature just is what it is.
The thing is they have so much money they can't buy enough. Even if all they do is consume, consume, consume they will still be trending upwards. In effect, every yacht has a negative price tag.
It bears the same hallmarks as any other addict: the next hit has to be even bigger than the last, and everyday enjoyments in life are practically invisible to them. Their drug of choice may be different, but the outcome on their life, relationships and society is largely the same.
To clarify, I don't mean all humans want to keep all money for themselves even when filthy rich, I just mean that all humans are self-interested. The extent to which that governs our behavior of course differs and I agree there are people who willingly sacrifice to help others. A bit more in another comment: https://news.ycombinator.com/item?id=45683652
It's up to policy makers (i.e. government when it comes to taxation) to structure the system to mitigate the inherent self-interest that people have. Obviously that's easier said than done when the ultra-rich buy off the politicians, but human nature just is what it is.