Hard to say exactly but it causes dementia and increased aggression in humans as well, it's simply necessary for proper brain function. Brains need glucose to function and B3 is used in several vital functions related to both energy production and neural health.

It could also just be an instinctual trigger in hamsters that makes them think they're starving and tbf they kind of are.

What we can say is fixing the deficiencies almost entirely eliminated the cannibalism.