Why is bronchiectasis caused by smoking?

Bronchiectasis. Smoking mainly causes emphysema, which is damage to the alveoli and smaller airways in the lungs. Bronchiectasis is damage to the larger airways, which is usually due to a medical condition or lung infection, even in childhood. Smoking with bronchiectasis, obviously, would be particularly bad.
Smoking irritates. Smoking irritates the bronchi. It causes inflammation and can damage the bronchi and bronchioles ability to naturally clear out pathogens leading to bronchitis or pneumonia. Smoking causes lung injury resulting in emphysema, chronic bronchitis, and lung cancer among many other risks. Please don't smoke.