People are unable to be good consumers, they have no money, thus more layoffs occur. Capitalist believe that in order to succeed in capitalism, the market must expand. But this expansion cannot last forever. Just like a spinning wheel, friction will enviably make it stop. The fact that people become wealthy off capitalism its what eventually crashes the market.
Wealthy individuals are less dependent on the system, and thus less inclined to work.
With every upward cycle, a downward one soon follows. As people begin to starve, they are forces to sell all their material processions for what ever they can get just to buy food. In a depression, people will work for what ever they can get and are easily exploited. They are just trying to feed their families and are desperate for work. This need to work starts the wheel spinning again.