The idea behind end-stage capitalism is that capitalists have, by now, penetrated and seized control of every market in the world. This is important because capitalism requires ever increasing rates of profits or you will be consumed by your competitor. Since there are no longer new labor pools and resource pool discovery is slackening, capitalists no longer have anywhere to expand.

Therefore, capitalists begin turning their attention back home, cutting wages and social safety nets, and resorting to fascism when the people complain.

This is the end stage of capitalism. The point at which capitalists begin devouring their own. Rosa Luxembourg famously posited that at this point, the world can choose “Socialism or Barbarism.” In other words, we can change our economic system, or we can allow the capitalists to sink to the lowest depths of depravity and drag us all down as they struggle to maintain their position.

Of course, if the capitalists manage to get to space, that opens up a whole new wealth of resources, likely delaying the end of their rule.

Yeah, we aren't all crouching naked in a muddy puddle, weeping and eating worms while the rich fly high above us in luxurious jets. Not yet, anyway.