Do you have evidence to back that up? I can think of a number of examples to the contrary offhand: The French Revolution was preceded by a financial crisis and poverty, as was the rise of the Nazism in Germany. There's Mohamed Bouazizi, the poor and repressed fruit vendor who helped launch the Arab Spring in Tunisia. And even the Occupy and Tea Party movements that have each arisen in response to the economic situation within the US.
While the poor struggle to survive from day to day, disappointed middle-class people are much more likely to engage in political activism to get their way.
This dynamic was evident in the Arab Spring, where regime-changing uprisings were led by tens of thousands of relatively well-educated young people. Both Tunisia and Egypt had produced large numbers of college graduates over the past generation. But the authoritarian governments of Zine El Abidine Ben Ali and Hosni Mubarak were classic crony-capitalist regimes, in which economic opportunities depended heavily on political connections. Neither country, in any event, had grown fast enough economically to provide jobs for ever-larger cohorts of young people. The result was political revolution.
None of this is a new phenomenon. The French, Bolshevik and Chinese Revolutions were all led by discontented middle-class individuals, even if their ultimate course was later affected by peasants, workers and the poor.
I think both Occupy and Tea Party movements fit this model. College kids mired in debt who can't find decent jobs. Aging white middle class conservatives watching the financial class run away with the lion's share of economic growth (while being led to believe that's it's being siphoned off by immigrants, welfare queens, and gay married couples).
Also brings to mind the old "Revolution to Conserve" idea I was introduced to back in AP American History: