There are hundreds of reasons why crashes occur....and some are very subtle and hard to articulate....particularly when you are the one being confronted with them day after day. (....or night after night)
Commercial pressure is one, having weather go below your limits is one...fatigue is another...night time is a big one....flying over isolated and dark areas is another....unforecast inclement weather is another....variable unforecastable weather due to terrain is yet another. How long a list do we want to create?
The size and numbers of the holes in that old chunk of Swiss Cheese is what matters!