I would argue that they happened exactly because the brokers who made up those financial institutions understood the math perfectly well: They make huge commis

I would argue that they happened exactly because the brokers who made up those financial institutions understood the math perfectly well: They make huge commissions on CDO and other deals. They sell the bad debt to some other shmuck and walk away with cash in their pocket and someone else holding the risk. That's why it keeps happening. They get rich and get away with it every time.