Why is flexible structure more prone to collapse?

WInd loads are very minimal for open structures, just because they can pass through the structure without getting obstructed. But an enclosed building faces much higher wind demands and thus many times leads to collapse of structures. Many chimneys have collapsed under wind loads and bridges have also been a victim of it. Too much flexibility leads to too much deflection, this causes collapse and damage to the structure. So for wind prefer stiffness and stability over flexibility.