How and why they say long term use of inhaled corticosteroids decrease immune system ?

Says who ?/BS: Four decades ago steroid use in asthma was considered taboo. The accepted word was after 1st use the patient would not respond without them.The only available forms were IV/oral or injected. Side effects were common. When inhaled steroids came along it revolutionized treatment. Miniscule amounts directly in the lung cells did their good & broke down without significant blood levels.