I actually thought all airlines require it but some don't enforce. The reason is that in case of crash, it allows rescuers to be able to see in windows if need be.
"Carpe diem quam minimum credula postero"
Seven Seas Explorer - Miami - Venice - Mar 2017
Silverseas Explorer - Arctic - Aug 2017
Seven Seas Voyager - Rome to Beijing - Oct 2017
Seven Seas Mariner - Lima to Buenos Aires - Jan 2018
Silverseas Explorer - Siberia - Jul 2018
Seven Seas Mariner - Australia Circumnavigation - Dec 2018