It was more comfy to ignore the warnings
Indeed plenty of persons warned about the dangers in quite clear term and I myself wrote in a letter published by FT in January 2003 saying that “Everyone knows that, sooner or later, the ratings issued by the credit agencies are just a new breed of systemic error to be propagated at modern speeds.”
If there is an explanation for why the warning were unheeded it is because of too much utterly misplaced solidarity among peers and the fact that we allowed our financial regulations to be captured by a small group of fanatics in Basel.