Preflight, of course. (<---- sniffs the cheese in the trap, yet does not bite)
But that's
outside the scope of the sim, which concentrates on the
mission flying portion of the operation of the plane.
For the same reason, we don't have debrief rooms you have to go to to get your orders; we don't have after-mission debriefs (although having players "claim" kills to compare against what the server knows to be true... that would be interesting for events!

)
We don't need to "run up" engines, we don't need groundcrew to turn intertia handles, or sit on wings while we taxi. We don't have to sit in the pit while the crew fuel us up, nor endure hours of "cockpit-readiness"...
All these things happened in the real event... but they're not necessary to simulate in the sim/game, are they? No.
However, the few seconds during which you do or don't manage your prop pitch, blower, cowl flaps, WEP and other injectants, fuel tanks and fuel state.... all those could tell the tale on whether you survive combat. I might also add that these events happen DURING the MISSION, and so are within the purview of the mission. It might only take a split second to flip a switch or manipulate a control, but the penalty for forgetting to do it may be severe; every bit as severe as overlooking something on the ground during a preflight.
Admittedly, a lot of this is game design decisionmaking... but if your goal is fidelity or realism, I don't see how you can leave out aircraft management... or worse still,
simply pretend it didn't exist or wasn't a factor.