Quite possibly your doc is thinking part of the problem is inflammation in your lungs, which is helped by steroids. There are some non-steroidal options for lung clearance - perhaps you could ask your doc - many can get into a "rut" and tend to prescribe the same med by default. The other option (short of a trip to Denver) is to begin calling pulmonologists and asking directly if they have experience treating MAC & bronchiectasis.
Sue