Rating of Transformers (why KVA and not KW)

Transformers have a name plate fixed on them on which rated output, rated voltages, the rated frequency, cooling method are recorded. The interesting fact is that its output rating is expressed in KVA (kilovolts ampere)rather then KW (kilowatt). This is due to the fact that the  transformer rated output is limited by heating and hence losses in the transformer. The two type of losses in a  transformer are core loss and ohmic losses.These  losses depend on transformer voltage and current and are almost unaffected by the load pf, therefore transformer rated output is expressed in VA or in KVA and not in KW