To be honest I almost never comment on a HN post when I'm this uninformed, however here is my reasoning:

Since the crisis, people now have a much better idea of what's in mortgage-backed CDO's than they did during the bubble. The ratings agencies are also under much more scrutiny to properly classify the risk of these vehicles. On the consumer side of things, it's much harder to get a mortgage than it was before the crisis. Adjustable rate mortgages are much less common, don't have misleading intro rates, and don't make brokers sky-high commissions. I grew up in Miami in the bubble, and I remember every other radio ad was for no-questions-asked home loans. You just don't have that kind of culture now.