Perhaps they feel the Note 7 name has been completely burnt (sorry!) in the public's eye and any attempt to salvage it at this point would cost them more than they could ever hope to recoup from further sales.
The only other thing I can think of is they've identified an issue with the phone itself that's causing this and either they or, more likely in my opinion, their insurance providers aren't willing to take the risk putting any more into the wild.
The only other thing I can think of is they've identified an issue with the phone itself that's causing this and either they or, more likely in my opinion, their insurance providers aren't willing to take the risk putting any more into the wild.