In my sailboat racing days on the west coast, it was commonly heard that 1) the lightest containers were placed highest - completely obvious if you understand ship stability - and that those containers were not secured as well - again completely by plan. If the ship were to be hit from the side with an 80 mph blast of wind and a 70' wave, the more containers that broke off, the more likely they were of living, sailing to port and coming home. Everybody on board knows this. The lost containers are just an insurance report to be filed.
That 80 mph wind and 70' wave might sound like an exaggeration or once in a lifetime event. I used to do the calcs and issue the stability reports for offshore fishing vessels, some as large as 250'. Small ships. One of the criteria the vessels I wrote the reports for had to meet was called "Severe Wind and Roll". It was a calculation of how much stability was lost when the vessel was struck from the side by a wave in a storm. My specialty was calculating how many of the big Bering Sea crabpots could be stacked on deck and meet that criteria - ie how much money they could make and still come home. The container ships are no different, just bigger.