Based on WWII Soviet comments it is rather disturbing to blow the head off a tank commander when he is INSIDE his tank, and they cannot see what nailed him. The Soviets did this on numerous occasions and ensured that the Germans had to move slow and have infantry in front and beside the tanks. Germans report that the solid WHACK of a round hitting and seeing a 1/2" porthole open over your head gives pause to think about another line of work!
The idea in Korea was probably the same. Armor on most tanks is focused to the front or at most the frontal 60 degree arc (e.g. 120 degrees of heavy armor coverage) so the side ot the turret is much thinner. I have never heard of any being damaged as we fought with infantry all the way and ergo these teams were not likely to get a shot.
The AT rifles also make great antimaterial weapons (which is what they are being brought back to do now) as you can stop a vehicle at up to 2,000 meters with one.