I have noted the same thing. Two partial explanations come to mind but don't fully explain it.
1. Many of these segment the platform into two or more segments, weighing the front and rear axle(s) separately and then adding the results. Splitting it left-right is the other obvious move. Cuts the dynamic range by a factor of two or more.
2. Low bandwidth/long time constant. Watching the display settle it isn't too long, on the order of a second, but definitely enough to eliminate engine vibration and many other high frequency noises.