Yes, you're right, we should be careful with the wording here. I would also blame the system, where Physics PhDs were paid to put enough math in the product presentations to convince traders that the AAA ratings (for products with substantially higher returns than usual for such ratings) were justified. Of course, the resulting transactions earned all sides huge individual cash bonuses (large enough to allow them to achieve financial independence if they could keep the scheme rolling for just a few years, regardless of whether their employers would go bust), which may arguably have contributed to their willingness to turn a blind eye to common sense.