I've been wondering that all along- if this was simply an accident. I thought about some kind of planned repair or refurbishment too but I think it if were that they would have prepared something to conceal the hole (they could easily have hung another photo above the existing ones).
Nah, the way refurbs are going it would have been missing for 6 months or more. Plus there would have been a sign saying "The bell is not available today. Please enjoy our other Main Street attractions"