I’d imagine 20 years of pounding up and down heavily laden with as many tourists that could be jam-packed into would eat into the airframe life quite heavily,and the constant increases and decreases in pressure and temperature as the plane is constantly climbing and descending on short hops all the time would just worsen the effect,so it may be at the end of it’s metal fatigue life.

Or maybe I’m wrong…….I feel faint after posting that,better go lie down 😀