Final answer:
The main reason an economy can remain in a recession for an extended period, as per Keynesian theory, is due to low aggregate demand and the stickiness of wages and prices that prevent quick economic adjustments.
Step-by-step explanation:
According to Keynesian economics, an economy can get stuck in a recession for a prolonged period of time primarily due to insufficient aggregate demand and the stickiness of wages and prices. Insufficient aggregate demand means that firms lack the incentive to hire enough workers for full employment. Meanwhile, sticky wages and prices, which are slow to adjust to demand changes, can prolong economic recovery due to menu costs and the reluctance of firms to lower prices, leading to extended periods of high unemployment.
This perspective is captured in the Keynesian AD/AS (Aggregate Demand/Aggregate Supply) model, where a recession begins with a decline in aggregate demand and persists due to the flat nature of the Short-Run Aggregate Supply (SRAS) curve below potential GDP.