Bob Herbert gives us a taste of what some mortgage lenders were up to. Yes plenty of people snared in the mortgage crisis "should have known better" for a variety of reasons, but plenty were victims of fraud and deception.
I think a fundamental issue here is that culturally we've been trained to see banks as regulated beasts which aren't going to engage in bad behavior. So we trust them more than we'd trust a used car salesman. We're not aware that they can engage in corrupt practices and so we assume they aren't.
Oh well.
...adding, plenty of players in this weren't technically banks, but they were engaged in traditional banking behavior and thus seen by people as banks.