They shifted because the quantitative and qualitative progress (i.e growth of population and introduction of industry) changed the structure of manufacturing and consume. Science and spare time added a scale to this progression. But social revolutions came when masses felt absolutely hopeless and nothing to lose. That made the elites to introduce social guarantees, minimum wage etc. If the majority is sheeple, the rulers have no incentive to develop the country except the military power. Here is what we see in modern Russia, for example.