The bumping/reschedule of the booking could be due to a number of factors... No enough original demand for the flight (or its return), a change to the scheduled aircraft type limiting the availability of seats... Last booked first bumped... Any spurious changes to Batflu restrictions...
Any alterations may not have been specifically related to that route, but as a consequence of changes/disruption elsewhere.
The 'botched' repair complaint only serves to highlight a lack of understanding about how aircraft maintenance works.
Let's say, for example, that the aircraft arrived at Heathrow at 0845 with a defect for a faulty coffee boiler.
At 0855, once tha passengers are off, the engineer gets informed of detail of the fault.
0900, having established that a fault keeps tripping the breaker, the boiler is removed for replacement with a serviceable one. This is the quickest, easiest approach to fixing the problem and would be a decision made based on likely fault and speed of rectification*.
0910, the replacement boiler is fitted, but still blows the breaker.
Boarding gets delayed 5 minutes.
0915 further investigation reveals a fault where the boiler loom has chaffed behind the galley assembly.
0920 aircraft gets swapped as it is going to be quicker to change aircraft than wait while this one is repaired.
Flight gets rescheduled to the nearest realistic time whilst the aircraft is swapped.
In order for this to happen, the following takes place:
Decision is made to either change gate and move everyone over to the new aircraft, or the aircraft gets swapped at the existing gate.
Catering gates pulled, bags offloaded, crew transfer over (if their hours permit) Aircraft gets towed x2 (if they keep the gate) or busses arranged to transfer passengers/crew.
Crew board new aircraft and prepare it (again) for the flight, catering, fuel and bags reloaded, new flightplan is filed and slot rescheduled. Passengers board and the flight departs. Late.
A two hour delay is pretty reasonable under the circumstances, but also consider that that aircraft will potentially be two hours late for the rest of the day.
Factor in that effect over a fleet the size of BA or EasyJet with all the associated schedule changes and reorganisation and it is sometimes a wonder that anything arrives when and where it was planned to.
The water boiler example is just that, there are thousands of parts that could fail or get damaged that could be a simple fix or a total nightmare... Not to mention third party damage such as the loaders or caterers damaging the aircraft. Also aircraft run with Minimum Equipment Lists which applies to everything on the aircraft... If it already has a couple of defects and the minimum is exceeded by a failure on the inbound flight, then fixing the minimum item may not be possible in the available turn around time. And knowing about an issue before the aircraft arrives is all well and good, but you can't do anything about it until it is on the ground and unless it's an engine fault, until it is unloaded.
To expect an airline to have a spare aircraft and crew for every flight waiting just in case is insane, and financially impossible. They might have four crews on standby and a couple of standby aircraft, but if your flight is the third one to develop a fault at that point, you're going to be delayed.
* Again this is a made up example of how an issue could escalate. An automotive example might be that your oil light comes on. You establish that the level is ok, so you change the sensor as that's the next easiest thing. This doesn't solve the problem, so you check the wiring (these two steps are interchangeable) which reveals no fault. Now you're into physically checking the oil pressure, which turns out to be really low. Suddenly you're into pulling/stripping the engine to swap out the oil pump.
Similarly a snapped wheel bolt or having a flat spare when you get a puncture on the motorway. In France. On a Sunday.
Doesn't take much of an escalation to turn a five minute job into a two day one.