What the carrier does to bridge a gap in their schedule depends on a number of factors (in no particular order and their will be others):
- What their Terms & Conditions of Carriage say. These are set by the Board and define their liability.
- Cost. Wet leasing an a/c and crew is not cheap and charter operations usually make savings in their service, so that they can charge less to the customer.
- What the failure was and when and where. If you have one a/c go out of service, you can mix-and match a bit. Lose two and you are stretched. In this day and age, no one has spare capacity.
I agree that we are often fed manure but it appears that this is genuine. There was a long discussion thread here some months ago about the subject of being told the reason for a delay and we had some insightful posts from flight and cabin crew explaining why they often were not told and could not help. It was as frusttrating for them but there can be a long trail of events that combine to delay a given, flight.