It could be that humans were asking a lot from the gods, and Celestia retaliated in order for humans to be made aware of their place. The boundaries between the worshipper and the worshipped can be fragile, if boundaries were not established well.

[ speaking from experience here, somewhat. ]

It'd be easy to paint the gods as the bad guys here, but that doesn't mean humans are faultless either. [ a shrug. ] Are you really okay with people like us fighting against your comrades, though? If you can call them that at this point.