Why does America have worse economic inequality than almost any other developed nation? Because of the Republican Party. It’s that simple. Why is the Republican Party the way it is? That’s a more complicated question.
A short answer is that the Republican Party is the way it is because of a series of laws and judicial rulings and some unfortunate byproducts of our Constitution that allow them to be that way.
Winner-take-all elections, money as speech, corporations as people, no Fairness Doctrine, gerrymandering, the Senate, Super PACs, and racial and religious divisions and anxieties explain most of it.
Or, another way of putting it is that rich people have arranged things this way with an assist from our Founders and a bunch of plutocratic judges. The right has always been unnaturally strong in this country.