It's the governments that are in these 20%. Politicians are rich and often abuse power to gain more wealth. They won't do anything about the problem because they're a part of it. Without their laws the disparity wouldn't be so great in the first place.

It works like this: Rich people pay politicians directly or pay lobbyists to establish laws that favor them and give them more ways to make money. They become even richer than before and have even more money for bribes. Most of them are untouchable like those pharma companies that charge $2 million for a drug that cures SMA.