my perception was this all started since 2009 , so I guess people who do it (in some cases) are resembling the market crash. Playing psychology I suppose...
"Since the S&P 500 sank briefly to 666 on March 6, 2009,"
"The Dow closed down 666 points, or 2.5%, its biggest percentage decline since the Brexit turmoil in June 2016 and steepest point decline since the 2008 financial crisis"