My take on this kind of thing is, they are the sellers items, and can be disposed of whenever and however they see fit.
This is my take as well, except it extends to the fact that they can do this at any time for any reason--including changing their mind. It's not the first time it's happened to me, and certainly won't be the last. And ime, generally these type of things are less of an issue with transparent communication where both parties know where the other is coming from so it's a 'win-win'. I've never been the type of buyer that thinks that the only good deal is one where one party wins and the other loses--that just leaves one person upset.
It's nice that the OP posted here why they didn't want to sell the items anymore, but I would liked to have an opportunity to make it as painless as possible for the OP, even at some cost to me. I know every time I've tried to find 6x drives like this in the same condition, it's still around $4/TB at best, which made the value of OPs items $144 for me, and it would have been nothing for me to have thrown $70 in packaging and shipping to have these drives for $100 my cost.