Firms became big enough to simply stop production instead of lowering prices to sell off excess inventory. So, prices did not fall, but production fell as factories closed and more workers became unemployed. This made depression worse, not better. Thus, government must intervene. To increase production, spending must increase.
People are out of work or worried about their jobs.
So, no C increase . Business have a gloomy outlook and unused factories. So, no I increase . Foreigners are in the same situation. So no X increase .