The reason for that is actually mechanical! If the last wheel is correctly placed when the cam is at a certain angle, the lock can jam. The number range isn’t the same on all IRL locks, because the dial can be rotated differently to the cam - however it is common for real locks to not have the final number be set in some specified range to prevent any problems.
In the simulator, the contact points are always the same relative to the dial, and so the final number in a combination will always be outside of the same range.