I once asked a Sim Engineer the exact same question some 13 years ago.
20 minutes later,,,,, It boils down to games having multiple pre- made fixed scenarios. A FFS display on the other hand has to react to any random movement by the hardware, the " simulated aircraft".
This is many levels harder and multiple computers are used to make this without delay seen by the Pilot.
AND 90% is night and or IMC so who cares.
The main thing is simulator fidelity or accuracy.