When we first got pre-approved, I was absolutely stunned at how much the charter banks were willing to give us. It was so much I was convinced it was a mistake. Fortunately, a riding buddy is also an excellent broker, and he sat down with us and after going through our situation in detail, suggested we keep our budget to just over half of what we'd been offered. The lesson to me is that the banks know that people will pay their mortgage before any other bills besides basic food, and are happy to bleed every penny of that.
The bit I don't understand is that the banks stand to lose as much as anyone if there's a crash. The reality is, even accounting for insured mortgages, they hold more than a lot of homeowners do in individual houses, so if things take a big tumble, they're underwater with everyone else. Having paying debtors seems like a better plan than a glut of foreclosed properties. Maybe they know they'll be bailed out, so are happy to keep dumping fuel on that fire...