i doubt a bank would have in its self-interest a desire to knowingly make loans to borrowers it knew were strong prospects for default. banks don't make money making bad loans ... at least the ones who make loans for their own portfolio
there is enough blame to go around to home buyers who purchased the loans with the cheapest financing vehicle they could find (initially). for example, when you go to a car lot and ask the price the car salesman will likely tell you how much it will cost you per month rather than the actual price of the car. and that's because that is how most American buyers make their purchase decision "can i make the monthly payment". they don't question that it's a 6 year loan and that they could get more favorable rates by arranging their financing conventionally, BEFORE making a purchase. it appears they buy homes the same way - stupidly.
there are mortgage brokers who can offer great INTRODUCTORY rates, that tease an unquestioning buyer into signing on the line. since these yield a far greater return to the mortgage company, they pay the broker who writes them a higher commission. so, the broker has an incentive to sell you the most expensive product. this is not exclusive to the brokerage business. but stupid buyers - who only want what they bought without concern for the consequences down the road - line up to buy.
collateralized securities. with everyone getting into the housing market and needing loans to buy them some clever wall street folks recognized that by pooling these mortgages, which were secured by real estate, they could sell them to investors ... invididuals, pension companies, etc., and the returns on these were better than what the investors could otherwise realize in the bond market. in search of a higher rate of return, the investors could not buy them fast enough. mortgage brokers streamilined their process so that in many instances there was almost no documentation required to indicate that the mortgage borrowers could actually afford to pay for their loans. brokers didn't care ... they were still getting fat commissions.
then interest rates started to edge up. also, teaser rate periods started expiring. those weak credits started having a difficult time performing. rating organizations, which make money by establishing a quality rating for this paper, saw something was amiss, but so many mortgages were pooled into a single mortgage-backed security instrument the few problems were generally masked by the performance of the many. and after all, they make money rating these things highly ... low rated instruments don't sell.
pretty soon (as in recently) the non-performing portion of the securities became so significant that stand & poor's (and the other rating organizations) could no longer ignore the problem and started downgrading the ratings of the mortgage backed securities. think of what happens when you panic brake your car. you do everything to quit going forward, or at least to proceed safely.
so, investors recognized they did not need to acquire any more inferior paper. some had too much and went under; others will soon follow.
i think if you look, those banks which processed mortgages for their own portfolios are doing fine. those that bought mortgage backed securities - like citibank - are scrambling to survive. those were the idiot bankers, not the ones who processed using accepted banking practices.

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“Mayor Palin fails to have a firm grasp of something very simple: the truth.”

[Frontiersman editorial, 2/7/97]