It matters because it is the middle class that consumes in volume and drives commerce.
For example- poor people cannot buy enough automobiles to support an industry. A single wealthy man could buy dozens of cars, but probably only buys 2 or 3 or none at all. Still not enough to support an industry.
It is the thousands of people in between who together buy thousands of cars.
You want a more equal distribution of wealth in order to have a large consumer class.
Having said that, it is not the wealthy “class“s fault that middle class jobs have disappeared. It is globalization of industry and technology.
You cannot engineer a thriving middle class