What this video fails to mention, or at least that excerpt, is that they took these risks while originating loans because the government was guaranteeing each and every single one.
Not only that, but they lowered the minimum standards of a qualified mortgagee at Fannie Mae and Freddie Mac, who bought these pieces of junk by the truck load.
This was caused, at its very essence, by the Federal government. No one asks, "why would they risk it all?" They just say they took "excessive risks." Fact is, they didn't take any risks, because it was all guaranteed. The only one taking the risk was the tax payer, holding the bag for decisions made by Mr. BagOfShit Frank and subsequently imposed on the quasi-governmental agencies Fannie&Freddie.