You know what I realized?
Eight and War never expected to live long enough to regenerate. In Eight’s case that was true. Had he not landed on Karn he wouldn’t have.
Nine and Eleven welcomed their regenerations. Even though their companions at the time couldn’t understand and didn’t want them to change, they embraced the change.
Ten and now Twelve fought their regenerations. They didn’t want to change. They liked who they had become and were scared to leave.
I wonder how Thirteen will react when her time comes?