The housing meltdown happened because there was a housing bubble, and the housing bubble was mostly created by the Government trying to artificially and aggressively influence the market so "everyone can have a home". That's the source. That the banks got involved in it later on and wanted to make easy money is just a symptom and an effect of the initial cause.
Of course, the US government magically controlled the housing markets in Britain, Spain, Ireland, and a number of other countries which experiencec similar housing bubbles and crashes. How'd that work?
Here in Australia, there's been a great deal of consternation that the "Big 4" banks no longer closely follow the movements in the cash rate set by the Reserve Bank (our central bank). This is because central bank funds have fallen to less than half of the cost of funding for our banks -- they mostly get their cash from the US and relend it Australians.
When the crisis first broke, Australian bank rates rose even while central bank rates fell. And that's because international finance became much more expensive.