'This makes me wonder why Amazon, in all their analytical genius, isn't cracking down on this when it's so blatantly obvious.'

Cynically, turn a blind-eye to misdemeanours of third-party sellers so long as there is data to be mined. Gradually replicate best-selling merchandise through your own-brand labels and then slowly dispose of the third-party sellers whilst retaining evidence of how they were systematically breaching the program terms in order to mitigate any chance of a class-action law suit.