I can certainly see why Carolina might have had some reservations about keeping him around and his potential arbitration award.
They're a contender in win now mode, so along with whatever they would've had to pay Ned, they'd also have to pony up for a solid 1B option that they could trust to carry the load if Ned has a sophomore slump or worse, goes full Blaine Lacher. Carolina probably wanted him to take something in the $2.5M range for a year to play a 1B role platooning with a veteran to see if he can repeat this past season and then get him signed up with starter money and term on his next deal.
With a completely clean slate at the position going into this summer, I'm betting the Canes want some stability in net after almost a decade of a revolving door to find a successor to Cam Ward. Not sure where that option comes from though... Grubauer? Rolling the dice on Andersen to get back to being decent starter behind a much better D and outside of the microscope in Toronto? Revisit their interest in Gibson?
I think where Carolina screwed up was allowing it to get out that they didn't want to qualify him. Basically tanked his value with teams knowing they could just wait till he hits the UFA market if the trade price was high.
None the less, it's still a great trade for the Wings. There's certainly risk that he could regress from last season, but the Wings still have Greiss to platoon with him, and they didn't pay a whole lot or commit to him longterm. So they have room to assess as they go along. But obviously I hope that in terms of Yzerman acquiring a young goalie, Ned trends more toward Bishop than Lindback.