In the current economy by necessity labor and capital are both required, and when capital tries to subjugate labor there tends to eventually be a violent reaction.
Given the dependency on labor it has been hard to fully centralize capital. Labor can unite to unseat the biggest monopolies.
I don’t see any such safety valves once you cross the rubicon into a fully automated self-sustaining people—less system (however far away you might think such a thing is). This makes for scary, dystopian outcomes if power happens to concentrate in the wrong way.