Why is erythropoietin secreted in larger quantities in patients with anemia or anoxic stress?

Erythropoietin is secreted in larger quantities in patients with anemia or anoxic stress because it prompts the bone marrow to form red blood cells. 

Erythropoietin, a hormone, is produced by the kidney. The kidney cells can detect whether the blood that travels through the kidney has low oxygen levels. If the blood has low oxygen levels, the kidney cells make and releases Erythropoietin. 

Erythropoietin is identified as a prime regulator of red cell production.Its 2 major functions are 1) Promote red blood cells development, and 2) Initiate the synthesis of hemoglobin. The hemoglobin is the molecule within red blood cells that transports oxygen.