> Subprime loans blew up because it was a bunch of opaque securities (mortgages sliced and diced together) that lenders thought were safe, but really weren't

Not quite. They blew up because the opacity meant nobody could verify that their paper was safe. That made them unsaleable. In the end, AAA-rated crisis-era paper all paid out and almost all of them paid out on schedule. But that doesn't help you if you need to fire sell them today.

Put more succinctly, a lot of people assumed that because Treasuries are highly rated and super liquid all highly-rated paper could be counted on to be liquid. Lenders thought the safe paper was liquid. In the end it was just safe.