The author mentions the French revolution, and that is a really important thing for the elites to understand. Class mobility -- as much as it existed because for a lot of people it didn't -- is what keeps the heads of the elites attached to their bodies.

When the system gets destroyed, and when the wealthy extract all the wealth from society, a lot of desperate people start looking for reform. And when the wealthy control and limit all means of reform (buying politicians, limiting free expression on social media, etc), reformists realize the only remaining path is revolution.