it's not really a matter of switches, availability, etc, but the actual flying characteristics are absolutely incorrect. For example, the 737 and the DC-9/MD-88 replica's on FS fly the same, but anyone with 5 minutes of experience in the aircraft knows that these two planes, in a lot of ways, are like night and day.
Like the 737 is like flying around a extra squirrely Cessna with very light requirements on the control inputs. Whereas the DC-9/MD-88 is a lot like trying to fly a heavy diesel truck with flat tires and absoltely requires two hands on the control at times.
On final approach, the 737 is pretty neutral, but the MD-88 is like trying to stand and balance on a basketball.
Flight Sim doesn't even come an iota close to the actual aircraft.