OK, I'll do my best: Economies of scale.
Consider two toy economies: One in which purchasing power is fairly evenly distributed among the population, and one in which it's concentrated via a power-law distribution into the top 1%, and 0.1%, etc.
In the first case, the quantities of mass-market products demanded will be much larger, because more people can afford to purchase them. This means demand for things like cameras, cell phones, breakfast cereals, movies, video games software, etc, go up. However most of these are also things where economies of scale makes production more efficient as order quantities increase. Factories can invest in jigs, automation, and high-throughput lines to make enough quantity for everyone. The jobs that produce these goods also become better-paid, and easier to secure investment for, because order quantities are higher and less volatile. And doubly so for intangible goods like software, ebooks, music, and video games: production can scale to infinite demand, so there can never be a production shortage, but people who work in these industries can be better rewarded for their efforts because a bigger audience can afford to pay more.
So order quantities grow, and so do incomes, but inflation is relatively low because of the increasing efficiency of production. This means real GDP per capita increases greatly, and the population as a whole becomes materially more wealthy. Even though wealth is being distributed away from top earners, there are huge material rewards available to anyone able to supply goods and services to the masses, because the masses are able to pay for those goods and services.
In the wealth-concentration economy, those mass-production industries have to fight for scraps, because the top 1% has as much purchasing power as the bottom 99%, and the top 0.1% has more purchasing power than the 1% below them. More purchasing power is directed towards luxury goods: golf courses, supercars, yachts, country club estates, Rolex watches, art, private jets, and real estate. Production quantities are low and inefficient, and in the case of land, production is effectively impossible. Prices go up for these assets, but there is little productive benefit to the economy. The excess wealth of the 0.1% is put towards buying political influence, buying news media, and so on, which becomes another negative for society as a whole. Meanwhile an entrepreneur might identify a pressing need among the bottom 25% of the populace, where very simple things (eg. vitamins or eyeglasses) could create an incredible increase in social welfare, but they will not be able to secure investment nor be rewarded for such efforts because there is no profit in it; the poor cannot afford to pay.