Valid point.
What is required as minimum though?. And at which ports of call. What are the comparative factors for the price of a rotable component, general spares, tooling etc when it's needed against the delay cost.
An aircraft swap isn't a big delay but the punters may not come back. And then theres the 10 to 3 factor of the number of people tell others of a bad to a good flight experience.
Worst scenario is putting up all pax for a night. Whats that cost?.
Experience, not accounting, would say having the right gear and people inplace works far more efficiently.
If you pulled up to a servo and were told the pumps knackered and waiting for it to be fixed, wouldn't you find somewhere else and never go back?. Both garages charging same price.