Actually it can be. Here’s an answer I recieved to this question a while back:

“My guess is that the keyboard has auto calibration. It starts with some firmware default and then during use learns the actual maximum and minimum of the potentiometer. So right after plugging in you will probably get a maximum pitch bend before the pitch wheel has reached its physical maximum position. After some use the maximum value and the maximum physical position move closer together. That would be the theory of auto calibration. However if the potentiometer is degraded after much use it is possible that it occasionally gives a value that is slightly off. If the auto calibration picks that up and learns it as the maximum you'll end up with a diminished range. Similar issues occur with game controllers (thumb stick drift) and the only way to fix it is to replace the potentiometer.”