Greed has everything to do with it.
Most of us want money because it brings us security, comfort, and maybe even a little luxury, for ourselves and our loved ones. This is natural and wholesome, and no one should be ashamed of feeling this way.
But for some, it is the power that money brings they crave. They can be filthy rich, all their needs and wants guaranteed for all time, but they never have enough. They always want more, more, more. And what's worse, they have nothing but contempt for everyone who isn't just like them. They feel they are intrinsically superior to them and that that gives them the right to take from others.
These are the most dangerous people in the world, and they have always brought nothing but misery to the rest of us.