Why would you doubt the reason? It seems that they are playing the game and not blaming weather, airport, ATC or anybody else?
Having "spare" aircraft sitting around, fuelled and crewed is a hugely expensive overhead and an airline is not likely to have more than one (if that many). Even if they do have one it can only be in one place, at one time and that place is probably not where it is needed now.
The least lovely part of any package holiday is always going to be the flights.