Bribes and protection money
I think that regardless of which party gets what from who, the basic fact is simply that the private sector pumps loads of money into the government. In some cases, it's to gain some sort of special favor that one can't get in the marketplace, or to do something nasty to the competition. In other cases, more morally defensible, it's "protection money" to prevent something nasty from being done to you. Bill Gates gave almost nothing to politicians until the politicians showed him where the power is.
Unless government is stripped of the powers to influence the private sector to the extent it does, I see no way this will ever change.