Why don't lungs fail during pulmonary edema?

They often do. Pulmonary edema is one of the most common causes of respiratory failure. That's why we have ventilators and icus. Less severe cases of pulmonary edema can be tolerated well enough to avoid respiratory failure. Just like a rain, its a matter of degree. You can have a light shower, or a deluge and flash-flooding.

Related Questions

How long does a pulmonary edema caused by lung injury take to develop?

Lung injury edema. depends on the nature and severity of injury but if it's going to occur normally would be apparent within a few days. Read more...