Low interest rates -- Fears of deflation, the bursting of the dot-com bubble, a U.S. recession, and the U.S. trade deficit kept interest rates low globally from 2000 to 2004-5, according to Economist Mark Zandi.[20] The low yield of the safe US Treasury bonds created demand by global investors for subprime mortgage-backed CDOs with their relatively high-yields but credit ratings as high as the Treasuries. This search for yield by global investors caused many to purchase CDOs, though they lived to regret trusting the credit rating agencies' ratings.[21]
Pricing models -- Gaussian copula models, introduced in 2001 by David X. Li, allowed for the rapid pricing of CDOs.[22][23]