This is really an interesting question. The reason is that we model center to center in software, but we consider beam-column junction as infinite rigid. Taking the value at the face of column is also less around 10-20% and in some cases upto 25%. Hence, there shall be significant saving in steel. It is also technically true that beam-column junction is rigid, so we don’t consider the value of moment and shear force at the center that may increase the reinforcement usage.