I think it's because them boys have an armored rating of '1' and are thusly getting shot to shiza from the masses of Soviet tanks and assault guns...
I don't think the game designers understand armoured operations--we run into similar problems in WitP. Mech dismount in the presence of serious AT opposition. Having armoured transport allows them to stay mounted given infantry opposition, which motorised troops can't do.
I wouldn't criticize the design decision, it might be as suggested above by TAIL_GUNNER that it has to do with the armor combat mechanisms and might well be unintentional.
Mech inf staying mounted when fighting infantry is really only practicable in a pursuit/exploit situation. The real advantage of having armored transport is when storming enemy positions, and paradoxically, it has less to do with enemy fire than with your own artillery fire.
When you attack, you want the enemy suppressed by your own artillery so they don't shoot at your advancing troops. If you don't have artillery support, you might as well not attack if the opposition is anything like serious. The problem is that the artillery has to let up when your troops are to storm the objective, otherwise you risk hitting your own troops. The safety distance for direct hit + splinters is about 300 meters for unprotected troops. Troops in an an armored personnel carrier are protected from splinters, so you only have to allow for the safety distance of a direct hit, which is about 50 meters.
So if you time your advance and the artillery fire right, mechanized infantry will be at 50 meters from the enemy positions when the artillery lets up and they dismount and start their charge, while normal infantry will be at 300 meters. As can readily be understood, this makes a whole lot of difference when the enemy is hurrying out of his dugouts and manning the machine guns.
Note: I learnt this during the 80:s as a reserve officer commanding a tank platoon. I don't know if this was practised during WW2, but I have every reason to believe so. The Germans were masters at coordinating artillery fire and movement to attack.
Many people think of APCs as an assault vehicle with panzer grenadiers firing every which way from the top, but that is not its primary use at all. The greatest use of an APC in WW2 style large scale combat is as a mobile splinter-proof shelter. It should never be exposed to enemy fire, especially not anti tank fire. An Sdkfz 251 has thin armor and can be damaged by many WW2 infantry weapons, even HMGs.
There was a discussion which dealt with similar issues on the decision games PC 'war in europe' forum. It arose over the the different treatment of motorised units and 'panzer grenadier' units. The latter are given a slightly smaller printed movement allowance, but, unlike the motorised units, get to move in both the movement phase and mechanised movement phase which follows combat.
Not sure if it passes muster but the 'expert' opinion was that, by choice, mechanised units dismounted before combat, that only the support versions of the 250/251 series would volutarily enter combat, and then, mounting long range weapons, generally at a distance. The movement advantage aforded 'panzer grenadier' divisions was doctrinal, in that the PzGs would dismount relatively close to the fighting compared to their motorised equivalents and that their transport- whether truck or halftrack- was organic rather than temporarily attached from a pool, as was often the case in other armies.
It was noted that the Germans also had an equivalent of the motorised division, a unit that de-trucked far behind the lines and marched up to the front, not having been trained in the PzG role.
It does make sense. The half tracks of all armies were at most bullet resistant, even then, subject to spall. You wouldn't want to be in grenade range either.
Based on that, I think it wrong that truck or halftrack mounted infantry should normally be targetted together wit htheir vehicle. Any information on the range at which these losses occur?
“The end of democracy and the defeat of the American Revolution will occur when government falls into the hands of lending institutions and moneyed incorporations.”
¯ Thomas Jefferson