(Finance isn't my primary job, so happy to be corrected) Firstly, leverage. A lack of rules and enforcement allowed unreasonable amounts of capital to amass ar

(Finance isn't my primary job, so happy to be corrected) Firstly, leverage. A lack of rules and enforcement allowed unreasonable amounts of capital to amass around mortgage bets. Without the crazy leverage via derivatives, the mortgage crisis would have been "A lot of loans go bad and some people get fired." Limit via regulation. Secondly, capital requirements. My understanding is that mortgage-backed securities are treated preferentially in terms of where a bank legally can allocate capital. Consequently, as they had to find returns somewhere, they constantly needed to plow huge amounts of money into the market. Inflows of money >> smart money meant that price discovery broke down: those who cared were drowned out. You'd need to avoid structuring taxes, etc to artificially force capital into this scheme.