I was working in the housing industry for 30 years before it tanked, and, IMHO, the problems in housing are from two sources: the barely regulated mortgage BROKER portion of the lending community taking over the majority of originating. Parties doing loans who were in no way vested in the long term performance of these loans and who also were clueless about the markets in which they were making them. Local brick and mortar lenders, on the other hand, knew their markets and could look at an appraisal that was inflated and realize the value did not jive, then research it further. Once these wise guy mortgage brokers started dominating the market, looking only for point spreads and origination fees, then dump the loan, the market started to disintegrate. Mall storefront brokers, doing loans for anyone who could steam a mirror, looking at high risk loans as increased income, as a way to get a better point spread.
Then the economy started to collapse, DURING Bush Cheney, and people's incomes started to disappear, and the housing industry spiraled down even faster..