A lot of it is due to the housing boom in the West. You saw that in OR/WA as well, though not as strongly as CA/NV/AZ.

There are a few reasons for it. One is simply that those states have high population growth and thus demand for housing, even if it was overbuilt. It's hard to get a housing bubble going in states that are losing population.

There are often also constraints on building in those states that limit supply and thus encourage bidding wars for what is available. That is partly due to tight growth control laws and zoning rules, but not only that. Topography imposes real limits as many Western cities butt up against mountain ranges or water features, whereas there's nothing but the odd anthill to keep Dallas and Kansas City from sprawling the whole 500 miles between them.

I don't think that explains it all though. There seemed to be more of a culture of issuing risky loans to support frantic home overbidding in the West (and Florida), and whether banks were more like that due to cultural issues or local regulatory differences I don't know.