Quite probably most of us will never know what caused our bronchiectasis. In my case, it could be long-term asthma, multiple cases of pneumonia, exposure to copious amounts of paper dust at work for a number of years, exposure to asbestosis in my youth and teens, 50+ years of intensive gardening... Since Bronchiectasis is incurable and irreversible, I personally don't feel the cause makes a difference, any more than why I needed bilateral hip replacements when I was 54.
What I do feel is more important is figuring out how to live well with my Bronchiectasis - what are my best actions and precautions to keep me as healthy as possible for as long as possible.
Why are you and your pulmonologist looking for the cause?
Sue