Some hypotheses that comes to my mind:
1. A well funded player has built a statistical model of the statistical models of some hedge funds.
2. Industrial espionage.
3. Tools back-doored by developers (as seen in "Office Space").
4. Reversion to the mean (positive results of the model were largely randomness combined with a small sample size).
It's worth noting that many nation-states would have incentive and resources for hypotheses one and two.
