Interesting fact, but is it really necessary to go to those lengths? Surely something like a handgun or detonated explosive would be cheaper and just as effective (though less fun). I don't think this use case needs the vehicle to be armored.
As for "why artillery", how do you plan on getting explosives into the snowpack, especially under conditions of severe avalanche risk? Those areas of the mountains are inaccessible by vehicle even in the summertime. A tank can drive on a road and deliver the explosives where needed. They often target 20+ separate snowfields so being able to do it in a timely and efficient manner matters.
While the armor doesn't contribute much, it happens to be what the artillery gun is attached to. It would cost far more to rig some special-purpose vehicle. Sherman tanks are free, the government has loads of them lying around waiting to be scrapped, you just pay for fuel and upkeep.
Artillery works great.