[pdoktar]

Because as said, cluster munitions attack the top of the tank where its HEAT or Dual-Purpose HEAT warhead will have enough power to penetrate that thin armor. Also the tank is usually struck by several munitions, thus increasing the chance to inflict critical damage to the vehicle or crew.

Opinions are varied, but generally a 155mm HE shell will not certainly destroy a MBT. It will give it a serious shock and disable systems, but the chance of a direct hit is extremely small. So the idea of those cluster munitions is to increase or even assure the chance of a hit in a given area for a single shell carrying those cluster munitions.