Looking at this "from the pictures". I would say it is down to the sign maker/s.
looks like an example of what i was talking about in my other reply. sign companies stacking the face with more signs. either that or re-sheeting it with plywood making the face heavier and heavier with only a continually deteriorating wooden structure to hold it in place.
do not get me wrong, i know the recent winds will have had aided its fall. regardless, there is no disputing the load those old fixings are taking has continually been increased over time.