Heads up, Creators: On Dec 13-14 you may see a noticeable decrease in your sub count as we remove spam subscriptions. If spam is removed, you'll see a YouTube Studio alert: https://goo.gl/qGDBvX This should help give you confidence that the subs you do have are real fans!
The timing suggests bad things. I'm not saying that's the reason, all I'm saying is the way they timed it and announced it is a way of getting back at creators who said Rewind was a flop. Again, I'm not saying that's the case because that would be allegation without evidence.