Operating the machine gun turret on the Humvee/Tigr 7M and MBTs can be incredibly disorienting and difficult when the vehicle is on the move, as the turret isn't stabilized and bounces all over the place. In order to make it easier for the driver and turret operator to coordinate, this machine gun turret should be stabilized.
I can understand not stabilizing it for the Humvee/Tigr. However, I think it's absolutely necessary on the tank. If I'm on the machine gun for a tank, the driver trying to go evasive and get away from enemy engineers often means I can't give any accurate covering fire for them, which has resulted in an enemy engineer being able to get close and kill us anyway more than once. A tank should not have to hold still for its machine gunner to provide effective defensive fire.
If nothing else, trying to engage targets with an unstabilized machine gun turret while on the move can be disorienting; I can imagine it can be outright dizzying or nauseating for some people.