There are five reasons the housing crisis happened.
1. The wrong homes were built. We all know what a McMansion is. Ronald Reagan taught America it was necessary to be rich. Builders wanted some too, but the problem here is, even though homes are vastly more expensive now than they were when Eisenhower was president, the profit margin in a well-built 1500sf home is about the same as it was in 1956. Unless something was done builders were going to have to continue living in modest homes and driving Buicks. The solutions were to vastly increase the size of the structure, increase housing density to minimize land usage, and add more and more luxurious amenities to the homes as they were being built. As a result, the average price of a new home increased from $76,400 in 1980 to $305,900 in 2006. (
http://www.census.gov/const/uspriceann.pdf)
1a. The existing home market wasn't immune to this either. In the old days when a homebuyer couldn't afford new construction he would opt for an existing home. Enter the house flipper. By purchasing rundown homes, doing superficial maintenance to them and reselling them at new home-like prices, house flippers caused all homebuyers to have to buy into an inflated marketplace.
2. Prior to 1980, there was a correlation between the price of new homes and the income of the people who bought them: as income went up, people bought larger and/or nicer homes. That didn't happen during the Reagan Eighties and in the following administrations. American manufacturing--once the source of a vast number of good-paying jobs--gave way to foreign manufacture, and the domestic manufacture that remained often moved to low-wage "right to work" (or, as I like to put it, "right to get fired") states.
3. So we're dealing with a two-pronged problem: less income to spend on more-expensive homes. Here's where the mortgage people come in. There are some circumstances where exotic financing makes sense. Take the much-maligned "interest-only" loan, where the homebuyer pays only the interest on the note for a specified period of time. If you have a lot of money, quite often it makes more sense to take out an interest-only loan than it does to pay cash for the house. (I know: huh? If you've got five or six million dollars and you know of a secure investment that will pay you ten percent or so for the next five years, the magic of compound interest will let one of those millions turn itself into more than a million dollars.) Everything's great until you start selling interest-only loans, negative-amortization loans (where the principal amount actually goes UP during the life of the loan) and other similar speculative mortgages to people who really should be in a plain, boring 30-year fixed note. The only advantage to them accrues to the banker: he can issue a $300,000 loan to someone who really can only afford a $125,000 house. And to those who say the people signing for these loans should have "known" they couldn't afford them, think: if a woman in a $2500 suit tells you that you can afford a particular home, you'll believe her.
4. Mortgages are securitized--the mortgage company combines $10 million worth of mortgages into a tranche and sells bonds against it--and have been for a long time. If you tranche selectively, by mixing prime-rate paper from wealthy areas with subprime shit so bad Michael Milken wouldn't have bought it, you can turn a portfolio of really shitty mortgages into first-class paper. You then sell Credit Default Swaps against these tranches. First you sell a CDS to anyone stupid enough to buy these mortgage-backed securities, then you sell CDS to speculators, then you tranche the CDS and MBS into yet other derivatives. By the time you're done, a $100,000 house is good for about $2.5 million in derivatives value.
5. And then when the inevitable happens--when Joe Homeowner's exotic loan's interest rate resets and Joe can't afford to make his house payment, and the same thing happens to a million Joes all across this great land of ours--we have a mortgage crisis.
You can spin this crisis any way you want and it all comes down to one simple fact: the root cause of the mortgage crisis was the need to sell quarter-million-dollar minicastles to Walmart employees.