Forget about the exploit itself. Why are people trusting two young nobodies (Day and Kellar of Indexed Finance) with so much money in the first place? Ok, so Day has some decent academic credentials, but he's just one person. Who was doing risk analysis? Which independent experts analyzed their algorithms? Which accounting firm audited them? Where's the oversight? These two guys whipped something up, threw it out in the wild, and the masses fed tens or hundreds of millions of dollars into it without a care in the world.
This is how crypto operates. Buyer beware.