Tandem Charge HEAT rounds

The title basically explains it. I'm relatively new to the the tank world, and my question is that as tank round were developed, why did tandem charge ATGMs become popular while unguided tandem charge HEAT rounds never really exist? I know some Russian tanks can fire ATGMs out of their barrel, but why that? It seems like with the advent of cope cages, tandem charges might be more useful than top attack munitions