“The sages decreed”! Better take a look at what Jesus thought of the man made laws that had been added to the Torah.
Yes, I know. Does this mean that you acknowledge Torah observant Jews offer prayers for the dead and that now you are going to attack them because both the Orthodox Christians and their elder brethren, Orthodox Jews (often even nonOthodox Jews also say Kaddish for departed close relatives) offer prayers for the dead while Protestants and all their derivatives do not ?