we are not all in it together.
When our economic policies helped the middle class, they hurt the rich. In the 1950s it was a lot harder to get rich than it is now, largely because of tax rates up to 90%. Cutting those taxes helped the rich, and helped a lot of people get rich. But there is no evidence that they helped anyone else; since Reagan's big tax cut the poor have struggled and the middle class has been treading water while the rich get richer at a bewildering pace.
So far as I can tell, it is simply a myth that the right economic policies will help everybody. Rich, poor, and middle class really do have different interests, and policies that help one group will probably hurt the others.