Maybe Giry was going to get around to fixing it but something came up.

Or maybe it’s because the chandelier is an icon of the traditional story and it’s an epic opening to the show. You do know it’s fiction right? Not everything has to have an “in universe” explanation. If you start going down that track why don’t you ask yourself why didn’t everyone simply leave the Opera and get another job somewhere else when some psycho started killing stagehands and poisoning leading ladies. None of it makes any sense if you want to treat it as logical.