I could imagine that having periodically changing loads like rush hour traffic could cause a critical failure state. The slow flexing between day and night even

I could imagine that having periodically changing loads like rush hour traffic could cause a critical failure state. The slow flexing between day and night eventually causing something to deform/crack/shift to the point that the next big traffic load causes a collapse. If prior NTSB reports are any predictor, we'll eventually learn all about the confluence of things that led to the collapse.