Just had a fairly successful Good Till canceled + Variations item suddenly end. I was wondering why the item ended, because I did not cancel it. It had several sales in November, so it should have been eligible to stay listed....
Thus, the best reason I can figure out is not every variation had sales, and thus the item ended. That seems to be very much not working as intended, to lose sales history / ranking on a successful listings, just because not all the variations are selling.
It could be some other reason though, but that's my best guess.