Why sinus infection takes a long time to heal?

Chronic sinusitis: Chronic sinusitis(CS) is common condition in which the sinuses around nasal passages become inflamed and swollen for at least eight weeks, despite therapy attempts.It interferes with drainage and causes mucus to build up. CS may be caused by infection, but can also be caused by (nasal polyps).CS most commonly affects young and middle-aged.Antibiotics sometimes necessary for sinusitis, not always.