In order to guarantee that flights are not cancelled, the airline would have to add a whole raft of risk mitigations, such as a spare plane, spare crew etc in standby.
Correct.
I know when I was in the industry even the large airlines would be pushed to have more than one or two spare aircraft with crews at base…some days it was “nil stock” by midday (even with the best maintenance aircraft bits break…not safety critical bits but bits Mr Boeing or Mr Airbus say are needed to work before going flying….)
More spare aircraft people say?
Well it’s maybe worth being aware a short haul aircraft these days easily costs over £50,000,000 to buy, maybe $10,000 a day plus to lease (which is more likely how it’s done).
Working hours regs mean to have flying staff providing 24/7coverage off short notice standby you need actually multiple crews ( the duty hours clock for a crew on standby at the airport is running down even if they are sat in the offices).
..and the real killer is of course that to give perfect coverage, to try avoiding >3 hour delays (the 261 trigger), you’d need a spare aircraft and crews at every station on the network.
So it doesn’t matter whether it’s BA or a LoCo, “Gold plated airways inc” or “what it says on the tin ltd,” no airline on earth is going to do that…
So delays will continue to happen, the airlines generally do their best at service recovery but can’t do the impossible so have simply factored EU 261/comp into their ticket prices.