How does Stoller explain why since the 1970’s there’s been massive turnover whether you look at the largest 10 companies, the largest 100, or the largest 1,000?

He's right. The very reason free markets don't exist is the same exact reason why communism doesn't work in practice. All markets collapse until there's a few dominant businesses (ie monopolies), just as how society naturally forms governing hierarchies. And this is easy to see how they're opposed. All you have to do is look at how there's only 4 types of governments based on how decision making power is distributed, and that democracy is actually closer to communism on that spectrum rather than dictatorships, and then see how monopolies behave quite like dictatorships.

That said, true dictatorships rarely work in practice but for different reasons as to why communism doesn't work. Which is why, when it comes to organizations, almost all are in fact oligarchies in practice, despite whatever they're called. This is known as the iron law of oligarchy. Notice the term: oligopoly? Go look at every industry and there's near always an oligopoly.