There's no repeat business in play. If the legit seeds were sold to a different set of farmers, those people would be repeat customers. The loss of the black farmers doesn't really matter. If the goal is to acquire the farmers' land after they're forced to sold then you don't want repeat customers, you want them to struggle.
And as I said to Mick, we have to assume that the distributor doesn't believe he will be caught...if he thought he would be caught, he wouldn't commit the crime. So, either the distributor can sell to a new set of farmers, acquire the farmers land or convince the farmers to give the distributor a 2nd chance (probably the preferred option since another batch of flawed seeds brings the land closer to sale).
This is a fairly common business fraud that you see across many industries. A distributor misrepresents the product to fatten their profit margin. And they usually get away with it for years until their greed leads them to take one risk to many or water down the product to a degree that they can no longer reasonably explain away.
Here, they probably talk their way out of the problem except for the university testing.